Locked memory card

You may have to large of a sd card. If it;s larger than 1mb then you may want to try using another that is smaller. See if that helps you out! Good-luck!!

As mentioned, you'll need to use recovery software. But first thing that's very important, take the card out of the camera and do not use it further until you've recovered the pictures. Below is a YouTube video of your freeware options, and here's more info on how to use these options, and where to get them.

Its a very common problem with S400,S410 and some others.

As a case study, see the following error message on the Canon IXUS 130 when trying to view some photos previously stored in the memory card SDHC

"Memory Card Error"

Every single photo stored on the memory card becomes inaccessible after the above error message. In addition, no more photos can be stored on the memory card. In short, the card can not be read or written.

Cause:
The above error message that makes all the pictures inaccessible is mainly caused due to corruption of the memory card. Reasons why you are responsible for the above error message is virus infection, interrupted read / write operation, and human error.

Resolution:
The resolution for the above error message is the format of memory card into the camera. The process erases all data previously stored and allows you to save the new data. While the format is a good resolution for users who do not require the old data, it is fatal to users such as photographers, detective agencies, etc, to save critical data on your memory card. However, the formatted data recovery day is now an easy process. It is therefore necessary to use an advanced part of third parties. A tool for image recovery is readily available on the Internet by one click.

Data Recovery is an application of high-end recovery that recovers data from almost all formats SDHC Card, XD and MMC. The read-only photo recovery tool also allows you to restore data in the defined location. The software runs on Mac OS X and Windows.

Check this link for additional details: Simple Fixes for SD "Memory Card Locked" or "Memory Card Error"

Hope helps.

take out memory card from camera, and connect memory card to computer using a card reader, then use this camera recovery software named asoftech data recovery
http://www.asoftech.com/adr/

The likely reason this keeps happening is that these cards weren't formatted in the camera when you first got them. However, don't do so just yet as formatting also erases the card. If you are using a memory card, take no more pics until you've recovered the photos, take the card out of the camera. This is to reduce the chance of you overwriting some of your "lost" photos. There are many good freeware photo recovery software options that are available to help you recover your photos. This blog article reviews and outlines several of the better ones. Now AFTER you've recovered the photos, format the cards IN THE CAMERA USING THE CAMERAS FORMAT FEATURE. Look for it, it's located under the "tools" menu (look for the item stating the card's memory capacity). This should rejuvenate both cards, and prevent reoccurrence.

Problems typically are pretty rare with Panasonic Lumix digital cameras. On those occasions where you do have an issue, though, look for an error message on the Panasonic camera for some clues as to how to fix the problem.
he seven tips listed here should help you troubleshoot your Panasonic camera error messages.

1. Built-in Memory Error error message. If you see this error message with your Panasonic camera, the internal memory area of the camera is either full or corrupted. Try downloading photos from the internal memory. If the error message continues to appear, you may need to format the internal memory area.
   
2. Memory Card Locked / Memory Card error message. Both of these error messages are related to the memory card, rather than the Panasonic camera. If you have an SD memory card, check the write protect switch on the side of the card. Slide the switch up to unlock the card. If the error message persists, it's possible the memory card is corrupted and needs to be formatted. It's also possible the memory card was formatted using another device that is not compatible with Panasonic's file structure system. Format the card with your Panasonic camera to fix the problem ... but keep in mind that formatting the card will erase any photos stored on it.
   
3. No Additional Selections Can Be Made error message. If your Panasonic camera allows you to "save" photos as your "favorites," you may find this error message because the camera has a limited number of photos that can be labeled as favorites, usually 999 photos. You cannot mark another photo as a favorite until you remove the favorite label from one or more photos. This error message also may occur if you're trying to delete more than 999 photos at one time.
   
4. No Valid Picture error message. This error message typically refers to a problem with the memory card. Most of the time, you'll find this error message when you try to play back images from the memory card and the memory card is corrupted, empty, broken, or has been formatted with another camera. To fix the memory card, you must format it, but formatting a memory card causes all photos stored on it to be lost. Try inserting the memory card in another device or in your computer and try downloading any photos stored on it before formatting it with your Panasonic camera.
   
5. Please Turn Camera Off And Then On Again error message. At least this error message says "please." This error message most likely occurs when one of the parts of the camera's hardware is malfunctioning, usually a jammed lens housing. To try to fix this problem, start by turning the camera off for a few seconds before turning it back on. If this doesn't fix the problem, try resetting the camera by removing the battery and memory card from the camera for at least 10 minutes. Replace both items and then try turning the camera on again. If the lens housing is jamming as the lens moves through its zoom range, try gently cleaning the housing, removing any debris or grime. If all of these steps don't fix the problem, you'll probably need a repair center for the camera.
   
6. This Battery Cannot Be Used error message. With this error message, you've either inserted a battery that's incompatible with your Panasonic camera or you've inserted a battery that has dirty contacts. Gently clean the metal contacts with a dry cloth. In addition, make sure the battery housing is free of debris. You sometimes may see this error message if you're using a battery that's not manufactured by Panasonic. If the third-party battery is working OK to power the camera, you probably can ignore this error message.
   
7. This Picture Is Protected error message. You'll see this Panasonic camera error message when the photo you've selected has been protected from deletion. Try working through the camera's menus to figure out how to remove any protection labels for the photo files.
   

Keep in mind that different models of Lumix cameras may provide a different set of error messages than is shown here. If you are seeing Panasonic camera error messages that aren't listed here, check with the user guide for your model of Panasonic Lumix camera for a list of other error messages, or visit the Support area of the Panasonic Web site.

You may try some photo recovery software to rescue the files on your digital camera sd card, here are some for your options.

Photo Recovery (for Windows)
Photo Recovery for Mac

Be careful: Before your pictures are recovered, do not attempt to save more files to the card in case the original files(your pictures) are overwritten.

the a 620 only goes up to 2 gb no higher

Some can't accept a card may be bad or incompatible. And while I asked if you formatted the card "in the camera", you just replied you formatted the card, but didn't spell it out and write "in the camera. Take the card and camera back to where you got it and ask them to show you working or ask for an exchange.

Have you formatted the card by using the camera to format?