Ok:
issue 1) is fixed by reinstallation (but anyway, there would be some dialog "your codecpack expired" instead of confusing dialog about my licence).
2) yes, it is very similar, it happens too when I switch from classic to aero, but also in some cases I can't describe (my described problem), because I don't find some reason for it (only >from time to time< by switching fullscreen to window). When i think about it it often happens when I play a lot of videos without restarting MM, I mean eg. 4+ hours of watching.
- it happens when i switch from fullscreen to window mode
- it is not connected with specific video file
- it happens when MM is playing videos for a long time
+ I will test it again if it was not caused by my expired codecpack like last time