To get around this you need to open the file manager as root. If you
don't have this option in the menu you can open a terminal and use gksu
nautilus or you can use sudo su then open nautilus from the commandline.

Once in Nautilus navigate to the Trash. If you are using 8.04 the Trash
has been moved to /home/[user]/.local/share/Trash. It is in a hidden
folder so Nautilus will have to have this option turned on.