funny thing is i ran into this same problem as you but with only version 5, though i don’t remember which build specifically. When a build works for me I usually set Avast to never download program updates, I turn off program update notices, and password protect the the update section.

Have you tried Installing Avast! in safemode DSREPAIR under a new Administrator account set as a member of a Workgroup? Worked for me in these settings.

If not, have you tried renaming the system OS name version to XP Home Edition in the registry, to temporarily make Avast! assume it’s not a server at all? Also, you must immediately undo this in the registry to avoid app. & system update conflicts.