I am trying to print a copy and I keep getting message.... Paper mismatch. Try changing the paper type/size or paper in tray. I am using the same 8.5x11 paper I have always used. Reference guide does not reference anything to paper mismatch. HELP!~~Mary reading papersize mismatch. does not work with changing paper.

You have a mismatch paper size. Document is not same as paper you have in copier. Try printing 8 1/2 by 11 document if doesn't print check printer preferences and adjust settings. Check copier paper trays make sure don't have special settings on them

Make sure the correct paper size is set on your computer before printing. With your file open, click File > Print > Properties > under Print Setup tab in the Paper Options area, ensure the correct Paper Size and Paper Type is set. Click OK to save the setting. Try to print again.

Paper mismatch errors occur because the product scans the width of the envelope before printing. If the paper size setting in the printer driver does not match the paper actually loaded in the product, the product reports a 'Paper Mismatch' error. The message saves paper and ink by preventing print jobs from accidentally printing on the wrong paper. For example, the print job might be for a 101.6 x 152.4 mm (4 x 6 inch) photo, but there is letter-size paper loaded in the product. The error message displays to make sure that ink is not wasted on the wrong paper type. try this out , disable the automatic paper type sensor.

1. Open the Print dialog box.
   1. In Word 2003, click File , and then click Print
   2. In Word 2007, click the Office button ( ), and then click Print .
2. Make sure that your product is in the Name drop-down list box, and then clickProperties .
3. Click the Features or Paper/Quality tab.
4. In the Paper type drop-down list, click Plain paper .
5. Click OK to close the Properties dialog box.
6. Click OK again to print the current print job.

Have/had the same problem: Getting "paper size mismatch" on the C4280 status screen, after we got a paper jam. Every time we hit OK and put in paper, Message about "Now printing Alignment page", it feeds through quickly, with nothing printed on the page and reverts back to Paper size mismatch. Finally got rid of the error, not sure how, but now when I try to copy anything, we only get the lower right postion of the document that I'm trying to copy. Printing from the PC seems ok.
Powered off and back on, and it is back to P"now printing alignment page, quick feed through and "paper size mismatch" error. AND
When copying directly from the glass panel,it will only print a quarter of the page -however it prints and coorectly if we print directly from the computer.
The problem is the paper size sensors. Remove the plastic access panel that is for access to the rollers in the back and has 4 rollers on it. There are two papaer sensors attached to the printer circuit board (PCB). The control arm for the sensor is a small plastic piece that extends slightly into the paper path above the PCB. The plastic can be broken when you are removing a paper jam. I stuck a small piece of a match stick in the sensor to keep it open (as though a wider piece of paper was passing throught the printer). I can't switch to smaller card stock, etc, but who cares, it works.
The copying problem is caused because the C4280 will not scan correctly until after it does the alignment phase.

Ignore the error and continue printing. The print job might still be acceptable even if the paper size and paper type settings are not an exact match.

1. Press Enter on the control panel to clear the error message.
2. Try the print job again.

• If these steps resolved the issue , you do not need to continue troubleshooting.
• If the issue persists , continue to the next solution.
  Use the HP product software, also known as the printer driver, to change the print settings for your paper size and type depending on your version of Microsoft Word.
  1. In Microsoft Word, click File , and then click Print .
  2. Make sure that your HP product is in the Name drop-down list box, and then clickProperties .
  3. Click the Features tab, or the Paper/Quality tab.
  4. Select a paper size from the Size drop-down list.If the required paper size is not in the drop-down list, follow these steps to create a custom paper size.
     1. Select Custom from the drop-down list.
     2. In the Custom Paper Size dialog box, type a name for the new custom size.
     3. In the Width and Height boxes, type the dimensions.
     4. Select the unit of measurement, and then click Save .
     5. Click OK to close the Custom Paper Size dialog box, and then click OKagain to close the Properties dialog box. NOTE: You must exit the Properties dialog box to apply your changes.
     6. Open the Properties dialog box again, and then select the new custom size from the Size drop-down list.
  5. Select the paper type.
     1. In the Paper Type or Type is drop-down list, click More .
     2. Click the desired paper type, and then click OK .
  6. Select the paper source from the Paper Source drop-down list.
  7. Change any other settings, and then click OK to close the Properties dialog box.
  8. Try the print job again.
     Paper mismatch errors occur because the printer scans the width of the paper before printing. If the paper size setting in the printer driver does not match the paper actually loaded in the printer, the printer reports a 'Paper Mismatch' or 'Paper too Narrow ' error.The error message might also display when you load the correct paper, just reinstall the printer driver if above procedure does not helps. Thanks. keep updated for any more query.you can rate this solution and show your appreciation.
     

if that is when your printing you have to check and be sure the paper tray size is set correctly. You press the machine status button and make sure, tray 1, 2 and the bypass are set to the proper size paper.

make sure that the the paper size set on the paper tray is correct. try to move the paper guides to another size and move it back to the correct size

Hello oyam26,
For any paper mismatch issue, first thing you do is try to set the paper type to plain. This will fix the issue in most of the cases.

gud luck

Check your printer preferences. Check inside the printer if it has some paper jam.
Cancel all your printer jobs, turn off the printer - Turn on the printer and try again

Are the print jobs being sent to printer all the same page size?

Are they all print jobs sent letter page size and your printers cassettes are set for A4 or something?

Your printer is asking for letter size paper, because any paper it has is not set to letter  and document that it is trying to print has been sent as that size.

Check what options you have on print driver on pc as far as Tray defaults, paper type and size settings

Check printer settings via its keypad as to tray defaults, paper size set for each tray and paper type, some printers have paper size switchs on their trays too.