hmmm, I have occasionally exact the same error message.
OS : W2K
Avast : 4.5.549
Internetconnection is WLAN
Theres nothing in the log, no unpxxx files, was happening also with earlier 4.5.x releases, started with the first official 4.5 release.
The error message comes from windows, not from avast. In my case the error message is in german - my OS language - but my avast installation is in english.
After the first time it has occured I have checked my memory and my harddisk. I can't see any scheme in the error message - every time I want to analyze it I don't get it.
Have not checked the minidumps till now - the next time I have it I'll go and check if I have a minidump and send it to Vlk.
I know thats not very helpful for analyzing it
br
Peter