system
3
I don’t know/remember exact requirements about older versions of Avast, but Avast 6 under Windows 2000 needs at least SP4 and Update Rollup 1 to be installed too.
Do you have your Avast database updated before the problem started? I ask because about a few days ago ( 2011AUG05 ) there was a problem under Windows 2k that was resolved by a manual full VPS update.