I would be suprised if that was true. SP2 updates alot to Windows, but if you have MSN7 installed on your system like you have now, then SP2 won't change that. SP2 doesn't make any changes to Messenger Plus! or Stuffplug itself either.
So if nothing is changed to Messenger, Plus! or Stuffplug when you install SP2, then why would anything in Stuffplug stop working? I haven't heard anybody else talking about this either. Just install SP2, if it stops working come back here
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EDIT: ashmanto was faster.