How to delete Time Machine backups from Trash
OK, so you deleted Time Machine backups via Finder and now you can't delete them from Trash.
First of all - you should NOT delete Time Machine backups in this way.
BUT all is not lost - to remove the backup folders from your Trash can, all you need to do is hold down the Alt key whilst using the Empty Trash facility.
Hope this helps.
Aperture 3, OS X Mountain Lion (10.8.2)