Im currently having the same problem. I have a Lexar 512.
I recently bought a SanDisk reader (the exact one on this page)
http://www.linuxjournal.com/node/6687/print
I went to copy a movie over and it corrupted all the files.
So I formatted it by click in PROPERTIES, FORMAT in winxp and set to FAT 32
Now i can put a movie on (ie southpark 150MB file), but when I go to put a second one on - it wont allow me to watch either - it says the files are corrupt or something?!
any ideas?!?!
I cant even seem to put MP3s on this card now...