Thumb Drive: Copies Files....Sometimes.

[Flyboy917]

I have a Lexar USB thumbdrive and Fedora has no problem seeing it. It loads, it unloads and it reads, and copies files....sometimes.
Three or four times now, I'll copy files from FC4 to it, take it to work, and the files arent' there. I always check (on the Fedora machine) that the files actually copied and it shows they have....but they really haven't. Other times it works without issue. What gives????