Hmmm, it seems the simple workaround to this would be to simply copy the files from the flash drive onto the desktop while you're viewing them.
While I don't know the causes of the problem or an outright solution (sorry), its possible that, however unlikely, that the data on the flash drive is corrupt. Flash Drives are meant for temporary and transfer media only, not for long term storage. If you can't manipulate the files outside of VLC (ie copy them to your local hard drive, or rename them or something), then its likely that your flash drive is corrupt.
