A great deal of the problems with SD cards are due to improper formatting. If you format the card using the normal Windows routine, it is apt to not work properly in all equipment or card readers because it will most likely end up formatted with the wrong file system.
In a previous post, Technics Player gave some reasons for problems. He suggested a low level format but did not detail how to do that.
If you are having problems with a card I suggest that you try the following:
1. Place the card in a good card reader (there are some junk cheapies out there that are being sold). You are usually OK with one made by SanDisk or Kingston.
2. Look at the card with Windows Explorer and make note of the disk identification that has been given to the card reader by the Windows operating system. Usually it will be D: or E: or F: ETC. It's a good idea to have one or two files on the card so that you can correctly identify it later on in this routine.
3. Let's suppose that it's E: for this exercise.
4. Go to "Start" "Run" and type "CMD" (without the quotation marks). This will get you to the black DOS window.
5. Type E: (or use the designation in step 2. Hit Enter.
6. Type DIR and hit Enter to make sure that you are seeing the card and not some other disk or partition on your hard drive.This is important because you don't want to accidently format the wrong item and lose all of the data therein.
7. Once you are sure that you are looking at the SD card, type "format E:/FS:FAT /X" (without quotation mqrks) and hit Enter. This command will release all 'handles' that can sometimes make a 2 GB card look like a 1MB card, ETC and will format the card to the FAT system which is the standard for SD Cards. Don't forget to replace the "E:" in the above example with your actual card drive designation that you found in step 2 above.
7. You will get a warning message that all will be erased -- and if all looks proper, hit Enter.
8. Try the card and see if it now works.

Good Luck,
Walt

[This message has been edited by Walt M (edited 01-21-2008).]