The setiface error is usually associated to corruption in avast when it is running and you try to uninstall.
Avast doesn't run in safe mode so it shouldn't be a problem to remove using the uninstall utility, try using this one, Download the avast! Uninstall Utility,
find it here it is called aswclear5.exe and it has uninstall tools for all avast versions in the drop down list, select 4.8.
When you ran the aswclear.exe from 'safe mode' what happened, any errors displayed ?