I guess Plus! just didnt run at windows' start up, the program should still be installed. Try this:
go to C:\program files\Messenger Plus! 3 and double click msgplus.exe. Then close and reopen your contact list and the menu should be there.
Then go to Plus! > Preferences. In the General options > local settings tab, there's a menu down there which says "Messenger attach method". Click on the menu and choose "default mode-forced".
You shouldnt have this problem anymore