I cannot secure empty trash
My iMac (3.2 GHz Intel Core i3, 16GB 1333 MHz 512MB, OS X 10.8.3 (12D78)) is set to remove trash securely. I have a rather full trash can, but when I try to empty the trash it prompts me to select whether to remove only iunlocked or all trash. I have tried both. It appears that it is starting, but stops immediately with no message as to why or that an error has happened. It simply closes the message box.
What can I do to get the trash off my computer?
iMac, OS X Mountain Lion (10.8.2)