Make sure the outlook.exe process is not there in task manager once Ol is closed.
can you also share the contecnts of the following key
and the same key under HKey current user
OL wants all related processes suspended before successfully closing ,most likely a plugin does not allow OL to close
please let me know if you need assistance
a good resource _http://msdn.microsoft.com/en-us/library/dd239276.aspx_