I think you could run as admin:

reg delete HKLM\System\CurrentControlSet\Services\tap0901 /f

After that, you should repair your avast! installation:
Can you try to repair your installation?
Go to Control Panel > Add/Remove programs > avast! antivirus > Remove. Then choose Repair function in the popup window (Repair).
If this does not help, you can uninstall / boot / install / boot again.