You could try using UNetbootin, the Ubuntu package is called
I have no idea what is the problem with the GUI -wrapper but this should work in Ubuntu, it works in Debian.
Check up the
sdNUMBER and then as a root overwrite the stick, be sure that you overwrite the right stick!
$ dmesg|grep sd|less # cat debian.iso > /dev/sdX # sync
Example: notice like
sdb, not like
$ sudo su # root@xyz:/home/xyz# cat /home/xyz/Documents/Distros/debian-6.0.5-i386-netinst.iso >/dev/sdb