Sounds like you're having midi issues? You didn't mention the source of the midi signals sent to those VSTi's, is it live input from you or from a midi track?
Either Cubase has again chosen the wrong midi driver (midi port filter fix), or you need timestamping (in device setup somewhere) or you are perhaps having issues with "live" midi signals input from you through scope to Cubase....hard to tell from the info provided.
Also this would have gotten more of a response in the 'Problem Solving' forum...