I have had this problem from the beginning with Elements:
Open project
Open midi-track with VSTi-instrument ( e g Massive or FM8)
Choosing a sound
In the VSTi; choosing another sound (shifting sound)
→ the VSTi window freezes. It is still possible to play that very sound but not shift to another sound again or go back.
At times the whole Cubase Elements freezes too and has to be restarted.
The problem is Cubase-related, since the VSTi:s work perfectly fine in standalone mode.
Well, all the VSTi:s with whom I have encountered this problem do not show this behaviour in standalone mode. Maybe it is to jump to conclusions saying the problem is only Cubase-related but it has only occurred in Cubase Elements 6 for me.
If 32bit plugs, it could be due to the bit bridge. J-Bridge may be a solution, you’d have to research whether your plugs are compatible with it on their site.