Try this - Missing VRDB 'i' icon, using notepad, edit the C:\Program Files\Alwil Software\Avast4\DATA\avast4.ini file, [VRDB] section, adding the following line, ShowTaskbarIcon=1 save the changes, the avast self-defence module will ask for confirmation, answer Yes and exit.
See example.
[VRDB]
MergeIcons=0
Disabled=0
ShowTaskbarIcon=1