Hmmm. Seems one of the avast KExts is crashing during unloading (part of the uninstall process) on your machine. Please provide a crash log. You should find it either in Library/Logs/DiagnosticReports (Mac OS X 10.6 or 10.7), or /Library/Logs/PanicReporter (Mac OS X v10.5).

You may use the tool below to uninstall build 30664. Note it will need a reboot so save all your documents and close your applications before using it.

http://public.avast.com/dev/mac-beta1/UninstallAvast.app.zip

Regards,
Mity