Cannot remove blacklisted email address

Avast Internet Security 5.1.889
Outlook 2007

Changes that I make to the spam filter’s blacklist won’t stay. There is one address, and it’s a legitimate email address that I regularly get mail from. I click the item and click “remove” and it vanishes. I OK out of the list, go right back in, and it’s back. I add an address so there’s two, OK out, come back in, and the one I don’t want on the list is still there, and the one I added is gone.

I don’t know how the one address even got there, but removing it won’t work and adding others won’t work.

I can’t figure out how to make changes to the list and keep them made. For now, I’ve just got spam filters turned off, but I’d like to use them.

I regularly use the computer as a limited user, but I’ve tried making the change as the Administrator also.

Suggestions appreciated.