Normally Not Authorized means that it is trying to mount with your permissions. Try going to a terminal and typing
This will put you in root
and get the /dev/sdyX (y will be partition letter IE a or b and X will be partition number.) Then try to mount it to /media
Code:
'mount /dev/sdyX /media/usb'
You may have to create the /media/usb folder space first. IF you can mount the drive then we know you have the correct filesystem driver and that it is truely a permissions problem.