I don't have that issue on my XP PRO SP3 system, spec below. Whilst I don't know if the latest build would make a difference, but Avast 10.3.2225 has just been released. I would suggest updating from the avast UI as there is less value in chasing a problem in an older version.
What is your operating system ?
Do you have WinPatrol ?
The reason I mention it a resent version messed with that very key, but I don't know if it would subsequently also mess with the permissions.