Can’t delete a calendar item I created

Outlook 2011 for Mac: I want to delete a recurring calendar item that I created, only it won't let me. It gets stuck in my outbox and says

"You don't have the permissions required to send messages from this mailbox."

Because I created it I can't "un-accept" the invitation, and it won't let me cancel it. It tries to send from my outbox every 90 seconds or so.

Is there a way to either figure out how to get my own permissions back for just this one item (all other items ok), or to just somehow delete this?

Question about Outlook Express