What update version of the software do you have?
What is the brand/size is your SD card?
Did you go through the 2-step update process completely?
How much free space do you have left on the SD card? (You mention that you may be dumping too many files onto the card, so do you have another SD card that you can play with, as members here try to find the solution to the problem.)
I updated to v 0.33c patch v13. I successfully completed both steps for the upgrade.I still have 1.7 GB free on a 2 GB card. I thought that the problem might be that I'm using a Kingston Micro SD card with an adaptor, but when I switched it out for a 1 GB pny card I use for backing up my books I got " No corresponding files found." (After the update I didn't transfer any books to the device itself- they're all on the card.) After pushing the reset button, it worked great, though it took awhile to get started- It has almost 1500 books on it. In case your curious that's 186 pages! Anyway, I'll just go back to using the other card and use the reset as needed. It's not a problem for me. I keep a paperclip on the case.