And here are the results:
1) "Try to record a phrase that ends up with stuck notes on the Virus into a MIDI clip. Do any notes get stuck when played back from the clip (to a Virus vs. to a softsynth)?"
-> No, the note are not stuck when I play back from the clip.
2) "set up a midi channel in cubase, with input from your keyboard and output to the virus"
-> As simple as it sounds, it fixed the issue! Instead of using ALL MIDI INPUT, I chose M AUDIO INPUT and ta-daaam it works....
For my defense I always used all midi input, and it always worked very fine until I installed Cubase 7, something to remember!
Thanks a lot Thetechnobear & Flabberbob for your help and support