Have you tried
fdisk? In a terminal, run
sudo fdisk /dev/sdx
/dev/sdx should be replaced with the device file for your flash drive. Once you get
fdisk open, type
p to list the partition table, and if the mysterious partition is listed, you can use
d # to delete it. (
# is the number of the partition, so e.g.
w writes the partition table back to the disk and
q quits. (hit
m for help)
fdisk fails, I guess you could just try zeroing out the first sector, which I think contains the partition table.
sudo dd if=/dev/zero of=/dev/sdx bs=512 count=1
/dev/sdx should be replaced with the actual device for your flash drive, will do that for you. You can increase the
count= number to write zeros to more of the disk, or omit it entirely to overwrite the entire disk. Needless to say, if you do this, you irretrievably lose any files that may have been stored on the disk.