WHY?

Does anybody have an idea why is cubase or superior drummer not letting me drag and drop grooves?
It happened just now. Everything was working fine until now. When I open other project everything works fine.
I adjust latency - it helped for just a while. Memory usage is 3,389,164 K for Cubase so this is not an issue. By the way - I shut down all other instruments and get down to under 2000000K with memory. Nothing changed…
Anybody?