It may sound stupid but I can't poweroff or halt my computer with backtrack 5 (installed on persistant usb 4GB).

Well if I logout and then type in:
sudo halt
sudo poweroff
the red backtrack 5 (desktop wallpaper-)sreen appears and nothing happens.
If I press "del" or "F12" now, it turns to the textmode but a bunch of errors appear and then it shuts down/halts. But next time I want to boot backtrack, endless errors appear.
I have to poweroff my computer by holding my "power botton" a few seconds. Cuz otherwise backtrack 5 doesn't work with the next boot...

here the errors:
"number"EXTZ-fs (loop1): error: ext2_lookup: deleted inode referenced: "number"
I really don't know what to do. Plz help.