I have the same problem. I recently updated avast 4 home edition to the latest one.
I am running an ancient computer win98se 166mhz 56mb ram.
I run the anti vuris with thorough scan archive enabled.
In the resident scanner I set the it scan all files and the box for files that will not be scaned I removed all except for swap.
When it starts up after the memory scan when the user interface pops up I get a active x control warning. So I choose not to run active x than the progam runs fine for about 30 minutes or so. Then it either stalls my computer or reboots it. The last time I got an active x warning my computer had a virus.
In the news I have noticed something about avast using winpopup. I also run spybot and it considers winpopup as spyware but it was not found when I ran spybot.
Checked the log found an error log. it read something like this odbc function sqlconnect failed odbc microsoft access driver could not find file.
I do not know if the newest version of avast 4 home edition has a bug or if some how I got an virus that avast can not find or attacks avast directly.
Thanks for any help.