At a guess, mount is guessing the wrong filesystem for the thumdrive -- Umsdos rather than Vfat. Run
mount (no arguments) after mounting your drive, and check what it's being mounted as.
Most likely, you'll need to change the thumbdrive entry in /etc/fstab from auto to vfat, e.g.
Code:
/dev/sda1 /usbdrive vfat rw,user,noauto,umask=0000 0 0
Cheers,
mj