When I scan transparencies, 1) The transparency to be scanned doesn't seem to lock itself into the MA-21 slide mount adapter the way it used to. I looked inside the adapter and everything seemed to be

You need to put a piece of white paper, the same size as your slide on the back of your slide. Your scanner doesn't recognize the edges of the transparancy (it is looking through it), so if you place a white paper on top of your transparancy it wil recognize the edges.

increase the space for virtual memory

The HP web site says the hpscanjet 2400 does not have a transparency materials adapter, so it would seem that you can not scan slide or negatives.

Please do the following to scan slides or negatives in manual mode of the Epson TWAIN:
For scanning transparencies in HOME mode - for EPSON SCAN models, not Epson Twain/Manual mode models.
1) In the program you are working from, begin the scanning process. If working in FULL AUTO MODE as the scan begins click PAUSE or CANCEL, then change "Full Auto Mode" to "Home Mode".
2) You will now see all Epson Scan settings displayed. If the scanner has not previewed automatically, click the large preview button to get a visual of what is on the scanner.
3) Ensure the settings on the Epson Scan are correct for what you wish to scan. For example, the DOCUMENT TYPE for transparencies must be either "Color negative film", "B&W Negative Film" or "Positive film"*.
* FILM here indicates that the item being scanned is transparent to light; this setting is also used for slide scanning. Positive indicates that the image is in true colors (ie the grass is green and sky is blue), whereas negative indicates reversed colors, as produced in some photo finishing processes.)
If the DOCUMENT SOURCE is set for a flatbed related option, ie PHOTO, the scanner is looking for reflective items and will not activate the backlight in the transparency unit. If the DOCUMENT TYPES for "FILM" are greyed out or cannot be selected, close the Epson Scan, reseat the power/communication cable connecting the base of the scanner to the transparency unit, then reopen Epson Scan and try again.
NOTE for PROFESSIONAL MODE users: DOCUMENT TYPE should read TRANSPARENCY for film scans.
4) Ensure the other scanner settings are correct for the type of scan you are doing. For example:
IMAGE TYPE should be color photo for all positive or negative color transparencies, or BLACK AND WHITE PHOTO for monochrome transparencies.
DESTINATION is unimportant, however you should select a RESOLUTION appropriate to what you plan to do with the scans. (There are no hard and fast rules for DPI. As a general guideline, if you are saving scans at original size, a resolution ranging from 400-600 DPI should capture enough information to faithfully record the image. If the slide or negative will be enlarged, you will need to increase this DPI accordingly. We have no means to calculate what your exact needs will be in this situation; you will need to experiment and view the output to gauge the appropriate input DPI from the scanner.)
PREVIEW. If your scanner is doing a THUMBNAIL PREVIEW, the slides will automatically preview and appear in boxes on the left side. Here, you can select or deselect the slides you wish to scan.
If you recieve a message that the scanner could not find the film, or you see in the preview that part of the scan is cut off, click the down arrow next to the large PREVIEW button and click NORMAL, then PREVIEW again. In NORMAL PREVIEW mode, the scanner will capture all information on the flatbed; you will then have to manually marquee or crop the slides you wish to scan. Use the left mouse button (click, hold, drag) to lasso one slide inside a box made of dotted lines, then click scan. Only the selected area will scan. Repeat this process for as many slides or filmstrips are on the bed.
5) Click CLOSE once scanning is complete. The images will now transfer to the application in use.

Please do the following to scan slides or negatives in manual mode of the Epson TWAIN:
For scanning transparencies in HOME mode - for EPSON SCAN models, not Epson Twain/Manual mode models.
1) In the program you are working from, begin the scanning process. If working in FULL AUTO MODE as the scan begins click PAUSE or CANCEL, then change "Full Auto Mode" to "Home Mode".
2) You will now see all Epson Scan settings displayed. If the scanner has not previewed automatically, click the large preview button to get a visual of what is on the scanner.
3) Ensure the settings on the Epson Scan are correct for what you wish to scan. For example, the DOCUMENT TYPE for transparencies must be either "Color negative film", "B&W Negative Film" or "Positive film"*.
* FILM here indicates that the item being scanned is transparent to light; this setting is also used for slide scanning. Positive indicates that the image is in true colors (ie the grass is green and sky is blue), whereas negative indicates reversed colors, as produced in some photo finishing processes.)
If the DOCUMENT SOURCE is set for a flatbed related option, ie PHOTO, the scanner is looking for reflective items and will not activate the backlight in the transparency unit. If the DOCUMENT TYPES for "FILM" are greyed out or cannot be selected, close the Epson Scan, reseat the power/communication cable connecting the base of the scanner to the transparency unit, then reopen Epson Scan and try again.
NOTE for PROFESSIONAL MODE users: DOCUMENT TYPE should read TRANSPARENCY for film scans.
4) Ensure the other scanner settings are correct for the type of scan you are doing. For example:
IMAGE TYPE should be color photo for all positive or negative color transparencies, or BLACK AND WHITE PHOTO for monochrome transparencies.
DESTINATION is unimportant, however you should select a RESOLUTION appropriate to what you plan to do with the scans. (There are no hard and fast rules for DPI. As a general guideline, if you are saving scans at original size, a resolution ranging from 400-600 DPI should capture enough information to faithfully record the image. If the slide or negative will be enlarged, you will need to increase this DPI accordingly. We have no means to calculate what your exact needs will be in this situation; you will need to experiment and view the output to gauge the appropriate input DPI from the scanner.)
PREVIEW. If your scanner is doing a THUMBNAIL PREVIEW, the slides will automatically preview and appear in boxes on the left side. Here, you can select or deselect the slides you wish to scan.
If you recieve a message that the scanner could not find the film, or you see in the preview that part of the scan is cut off, click the down arrow next to the large PREVIEW button and click NORMAL, then PREVIEW again. In NORMAL PREVIEW mode, the scanner will capture all information on the flatbed; you will then have to manually marquee or crop the slides you wish to scan. Use the left mouse button (click, hold, drag) to lasso one slide inside a box made of dotted lines, then click scan. Only the selected area will scan. Repeat this process for as many slides or filmstrips are on the bed.
5) Click CLOSE once scanning is complete. The images will now transfer to the application in use.

Yes there is

Please do the following to scan slides or negatives in manual mode of the Epson TWAIN:
For scanning transparencies in HOME mode - for EPSON SCAN models, not Epson Twain/Manual mode models.
1) In the program you are working from, begin the scanning process. If working in FULL AUTO MODE as the scan begins click PAUSE or CANCEL, then change "Full Auto Mode" to "Home Mode".
2) You will now see all Epson Scan settings displayed. If the scanner has not previewed automatically, click the large preview button to get a visual of what is on the scanner.
3) Ensure the settings on the Epson Scan are correct for what you wish to scan. For example, the DOCUMENT TYPE for transparencies must be either "Color negative film", "B&W Negative Film" or "Positive film"*.
* FILM here indicates that the item being scanned is transparent to light; this setting is also used for slide scanning. Positive indicates that the image is in true colors (ie the grass is green and sky is blue), whereas negative indicates reversed colors, as produced in some photo finishing processes.)
If the DOCUMENT SOURCE is set for a flatbed related option, ie PHOTO, the scanner is looking for reflective items and will not activate the backlight in the transparency unit. If the DOCUMENT TYPES for "FILM" are greyed out or cannot be selected, close the Epson Scan, reseat the power/communication cable connecting the base of the scanner to the transparency unit, then reopen Epson Scan and try again.
NOTE for PROFESSIONAL MODE users: DOCUMENT TYPE should read TRANSPARENCY for film scans.
4) Ensure the other scanner settings are correct for the type of scan you are doing. For example:
IMAGE TYPE should be color photo for all positive or negative color transparencies, or BLACK AND WHITE PHOTO for monochrome transparencies.
DESTINATION is unimportant, however you should select a RESOLUTION appropriate to what you plan to do with the scans. (There are no hard and fast rules for DPI. As a general guideline, if you are saving scans at original size, a resolution ranging from 400-600 DPI should capture enough information to faithfully record the image. If the slide or negative will be enlarged, you will need to increase this DPI accordingly. We have no means to calculate what your exact needs will be in this situation; you will need to experiment and view the output to gauge the appropriate input DPI from the scanner.)
PREVIEW. If your scanner is doing a THUMBNAIL PREVIEW, the slides will automatically preview and appear in boxes on the left side. Here, you can select or deselect the slides you wish to scan.
If you recieve a message that the scanner could not find the film, or you see in the preview that part of the scan is cut off, click the down arrow next to the large PREVIEW button and click NORMAL, then PREVIEW again. In NORMAL PREVIEW mode, the scanner will capture all information on the flatbed; you will then have to manually marquee or crop the slides you wish to scan. Use the left mouse button (click, hold, drag) to lasso one slide inside a box made of dotted lines, then click scan. Only the selected area will scan. Repeat this process for as many slides or filmstrips are on the bed.
5) Click CLOSE once scanning is complete. The images will now transfer to the application in use.

Please do the following to scan slides or negatives in manual mode of the Epson TWAIN:
For scanning transparencies in HOME mode - for EPSON SCAN models, not Epson Twain/Manual mode models.
1) In the program you are working from, begin the scanning process. If working in FULL AUTO MODE as the scan begins click PAUSE or CANCEL, then change "Full Auto Mode" to "Home Mode".
2) You will now see all Epson Scan settings displayed. If the scanner has not previewed automatically, click the large preview button to get a visual of what is on the scanner.
3) Ensure the settings on the Epson Scan are correct for what you wish to scan. For example, the DOCUMENT TYPE for transparencies must be either "Color negative film", "B&W Negative Film" or "Positive film"*.
* FILM here indicates that the item being scanned is transparent to light; this setting is also used for slide scanning. Positive indicates that the image is in true colors (ie the grass is green and sky is blue), whereas negative indicates reversed colors, as produced in some photo finishing processes.)
If the DOCUMENT SOURCE is set for a flatbed related option, ie PHOTO, the scanner is looking for reflective items and will not activate the backlight in the transparency unit. If the DOCUMENT TYPES for "FILM" are greyed out or cannot be selected, close the Epson Scan, reseat the power/communication cable connecting the base of the scanner to the transparency unit, then reopen Epson Scan and try again.
NOTE for PROFESSIONAL MODE users: DOCUMENT TYPE should read TRANSPARENCY for film scans.
4) Ensure the other scanner settings are correct for the type of scan you are doing. For example:
IMAGE TYPE should be color photo for all positive or negative color transparencies, or BLACK AND WHITE PHOTO for monochrome transparencies.
DESTINATION is unimportant, however you should select a RESOLUTION appropriate to what you plan to do with the scans. (There are no hard and fast rules for DPI. As a general guideline, if you are saving scans at original size, a resolution ranging from 400-600 DPI should capture enough information to faithfully record the image. If the slide or negative will be enlarged, you will need to increase this DPI accordingly. We have no means to calculate what your exact needs will be in this situation; you will need to experiment and view the output to gauge the appropriate input DPI from the scanner.)
PREVIEW. If your scanner is doing a THUMBNAIL PREVIEW, the slides will automatically preview and appear in boxes on the left side. Here, you can select or deselect the slides you wish to scan.
If you recieve a message that the scanner could not find the film, or you see in the preview that part of the scan is cut off, click the down arrow next to the large PREVIEW button and click NORMAL, then PREVIEW again. In NORMAL PREVIEW mode, the scanner will capture all information on the flatbed; you will then have to manually marquee or crop the slides you wish to scan. Use the left mouse button (click, hold, drag) to lasso one slide inside a box made of dotted lines, then click scan. Only the selected area will scan. Repeat this process for as many slides or filmstrips are on the bed.
5) Click CLOSE once scanning is complete. The images will now transfer to the application in use.

Please do the following to scan slides or negatives in manual mode of the Epson TWAIN:
1) In the program you are working from, begin the scanning process. If working in full auto mode, as the scan begins you will see a message that reads TO CANCEL SCANNING IN FULL AUTO MODE AND SWITCH TO MANUAL MODE, CLICK CANCEL. At this point, click CANCEL, then MANUAL MODE.
2) You will now see all Epson Twain settings displayed. If the scanner has not previewed automatically, click the full page preview button (icon of a paper with one corner folded down).
3) Ensure the settings on the right hand side of the Twain are correct. For example, the DOCUMENT SOURCE for transparencies must be either TPU: COLOR NEGATIVE FILM, TPU: MONOCHROME NEG or TPU: POSITIVE FILM.
FILM here indicates that the item being scanned is transparent to light; this setting is also used for slide scanning. Positive indicates that the image is in true colors (ie the grass is green and sky is blue), whereas negative indicates reversed colors, as produced in some photo finishing processes. (If you are scanning a black and white slide in true colors, choose TPU: POSITIVE FILM as the DOCUMENT SOURCE and BLACK AND WHITE PHOTO as the IMAGE TYPE.)
If the DOCUMENT SOURCE is flatbed, the scanner will not activate the backlight in the transparency unit. If the DOCUMENT SOURCE is greyed out and you cannot select a TPU option, close the twain, reseat the power/communication cable connecting flatbed to TPU, then re-open the twain and try again.
4) Ensure the other twain settings are correct for the type of scan you are doing.
IMAGE TYPE should be color photo for all positive or negative color transparencies, or BLACK AND WHITE PHOTO for monochrome transparencies.
DESTINATION is unimportant, however you should select a RESOLUTION appropriate to what you plan to do with the scans. (There are no hard and fast rules for DPI. As a general guideline, if you are saving scans at original size, a resolution ranging from 400-600 DPI should capture enough information to faithfully record the image. If the slide or negative will be enlarged, you will need to increase this DPI accordingly. We have no guidelines on this; you will need to experiment and view the output to gauge the appropriate input DPI from the scanner.)
PREVIEW. If your scanner is doing an AUTOMATIC THUMBNAIL PREVIEW, the slides will automatically preview and appear in boxes on the left side. Here, you can select or deselect the slides you wish to scan.
If you recieve a message that the scanner could not find the film, click the CONFIGURATION button and uncheck AUTOMATIC THUMBNAIL PREVIEW FOR FILM, then OK, and try the PREVIEW button (page with corner folded down) again.
In this mode, you will have to manually marquee or crop the slides you wish to scan. Use the left mouse button to lasso one slide inside a box made of dotted lines, then click scan. Only the selected area will scan. Repeat this process (manually crop then scan) for as many slides or filmstrips are on the bed.
5) Click CLOSE once scanning is complete. The images will now transfer to the application in use.

I have the same problem with my 4990. This began when I moved to a new computer running Vista. I've updated all drivers to the latest version including Epson Scan for Vista but the only thing the 4990 "sees" is reflective documents. Negatives are not recognized at all. I know this is probably a different problem from what you are having but the effect is the same.

Here they are for Mac and PC

Please do the following to scan slides or negatives in manual mode of the Epson TWAIN:
For scanning transparencies in HOME mode - for EPSON SCAN models, not Epson Twain/Manual mode models.
1) In the program you are working from, begin the scanning process. If working in FULL AUTO MODE as the scan begins click PAUSE or CANCEL, then change "Full Auto Mode" to "Home Mode".
2) You will now see all Epson Scan settings displayed. If the scanner has not previewed automatically, click the large preview button to get a visual of what is on the scanner.
3) Ensure the settings on the Epson Scan are correct for what you wish to scan. For example, the DOCUMENT TYPE for transparencies must be either "Color negative film", "B&W Negative Film" or "Positive film"*.
* FILM here indicates that the item being scanned is transparent to light; this setting is also used for slide scanning. Positive indicates that the image is in true colors (ie the grass is green and sky is blue), whereas negative indicates reversed colors, as produced in some photo finishing processes.)
If the DOCUMENT SOURCE is set for a flatbed related option, ie PHOTO, the scanner is looking for reflective items and will not activate the backlight in the transparency unit. If the DOCUMENT TYPES for "FILM" are greyed out or cannot be selected, close the Epson Scan, reseat the power/communication cable connecting the base of the scanner to the transparency unit, then reopen Epson Scan and try again.
NOTE for PROFESSIONAL MODE users: DOCUMENT TYPE should read TRANSPARENCY for film scans.
4) Ensure the other scanner settings are correct for the type of scan you are doing. For example:
IMAGE TYPE should be color photo for all positive or negative color transparencies, or BLACK AND WHITE PHOTO for monochrome transparencies.
DESTINATION is unimportant, however you should select a RESOLUTION appropriate to what you plan to do with the scans. (There are no hard and fast rules for DPI. As a general guideline, if you are saving scans at original size, a resolution ranging from 400-600 DPI should capture enough information to faithfully record the image. If the slide or negative will be enlarged, you will need to increase this DPI accordingly. We have no means to calculate what your exact needs will be in this situation; you will need to experiment and view the output to gauge the appropriate input DPI from the scanner.)
PREVIEW. If your scanner is doing a THUMBNAIL PREVIEW, the slides will automatically preview and appear in boxes on the left side. Here, you can select or deselect the slides you wish to scan.
If you receive a message that the scanner could not find the film, or you see in the preview that part of the scan is cut off, click the down arrow next to the large PREVIEW button and click NORMAL, then PREVIEW again. In NORMAL PREVIEW mode, the scanner will capture all information on the flatbed; you will then have to manually marquee or crop the slides you wish to scan. Use the left mouse button (click, hold, drag) to lasso one slide inside a box made of dotted lines, then click scan. Only the selected area will scan. Repeat this process for as many slides or filmstrips are on the bed.
5) Click CLOSE once scanning is complete. The images will now transfer to the application in use.