I did removed the avast 4.6 with the uninstall tool "Aswclear" and installed the new version, all if fine.
It's adviceable that you FIRST try to use the Add/Remove Control Panel and then the tool.
It will be better if Alwil change the behavior of this tool and show a window where the user can choose the Control Panel AND the tool itself with a message that use the tool ONLY in case of Control Panel fails.
It won't be so difficult... just add code for the link bellow:
C:\WINDOWS\system32\rundll32.exe <avast>\Setup\setiface.dll,RunSetup