Welcome from here, John - we all learn from these things.
I run XP SP3 AND teatimer, with Z Alarm and Avast 5.0.0545. The only thing I can recall, as I said, from over a month ago's upgrade, was having to manually set the firewall to allow Avast Service (I think it was!).
Google seems littered with this problem as you no doubt no
One post I saw reckoned Ashampoo was the culprit.
A thought - can you update any other security stuff?