Originally Posted by Billi
I think this is not a bug but a feature.
Actually, the back key should work as expected. If you entered a book from the main menu screen, that's where the back key should take you; if you're in a specific folder and open a book there, the back key should take you back to the folder. That's how it works for me anyway.
Do you have any files/folders with very long names on your card, as that is known to cause freezes (or rather, database update infinite loops). Usually happens when there is a path/file name that is around 200 characters in total.
Also try a different model/brand of SD card. For 4GB cards, make sure it's SDHC compliant and not the old SD standard which officially supports only up to 2GB.
If you have a digital camera or MP3 player or any other device which uses FAT filesystem and is capable of formatting SD cards, try formatting the card using one of those devices. It's a shame the iriver can't do that by itself - maybe I could make a mod for that, but it'd only work with wifi / Web Portal.