Hehe, that was strange. I killed the avast processes and restarted the application. I tried to update avast (but it gave an error which says that avast instance update is already running). I noticed it was a huge update. When the update was installed avast! started to work as it should and the problem is solved. I guess I downloaded and installed bad update in wrong time (maybe the update was pulled out) and the newest one is corrected.
Anyway this will remain a mystery to me. 
Regards,
Georgi