And what are you expecting to happen?

So instead of hitting Ctrl+D to delete an item, what happens when the
item is selected and you hit the Del key, or the "X" toolbar button,
or right-click on the item and select Delete?

Did you really expect a detailed response for such a vague question?
You didn't even bother to say what "not working" means, like the item
does not get deleted, Outlook hangs or crashes, you get an error
message, that you thought the item would get permanently deleted
rather than just moved into the Deleted Items folder.

Read the following:
http://66.39.69.143/goodpost.htm
http://support.microsoft.com/kb/555375
http://users.tpg.com.au/bzyhjr/liszt.html