Comment 12 for bug 227753

I had the same problem and found my solution here at http://www.blog.arun-prabha.com/2008/07/22/deleting-files-from-roots-trash-folder-in-ubuntu/. I did not have to re-install the OS.

Apparently when the network share drive fails to mount due to the fstab problem (network not up, drive will not mount), sBackup creates the backup in your root folder. The procedure at this site outline the steps to clear the hidden backup folder/file then describes how to delete them from the root Trash folder. I just cleared up 22 Gib of reported space. Kudos to Arun Subramanian’s Blog (Deleting files from root’s trash folder in Ubuntu)!

I hope this helps