I got this too. The problem seems to be with the preference pane of avast!. If you attempt to open the avast! preference pane it gives:
"Internal error!
An internal error occurred. You may find more info by opening the avast! application or by searching he system logs."
I'm running the latest build, 39915.
Edit:
The preference pane works, you have to access the preference pane in the Incompatible Software folder on the main drive. Double clicking the Avast.prefPane file to open resolves the problem for me at least.