Why is it some rules just won't work in automatic mode?

I have a rule set up in my Outlook (2002) to check mail when it comes in and
if the email sources matches a contact in the outlook contacts folder, it
should move the message to a outlook folder. The rule doesn't work on it's
own, but if I run it manually, it works flawlessly.

I have several other rules defined and they all work just fine. There are
no stops or anything else in other rules that would prevent the rule from
running. I don't get it!

Outlook is running under XP and connected to and Exchange server and I'm
running in non-cache mode