Outlook Outbox in XP

I sent an email reply, which was undeliverable, but Outlook still continues to try and send it when i Send & Receive my mail. The email does not show up in the Outbox where I should be able to delete it. I get a sending error task message. I have updated to SP1 & SP2 for XP Office. Why doesn’t the message show it’s stuck in my Outbox? Should I replace my .pst file? I couldn’t find anything in MS Knowledge base.