The correct name of this episode is "Forgoten Lady."

"Forgotten Lady," trust me, I have seen this episode a million times. The main character is an aging film star and she murders her husband for his money so that she can resume her showbiz career.

Well, Marcia, it could actually be either one of the episodes....Forgotten Lady or Make Me a Perfect Murder. Maybe Lady in waiting could give us a little more info to decide on which one it could be.
And Lady in waiting, you did very well with posting in a different language other than your own.

Lady in waiting said:"I just wonder about an episode which took place in a cinema. Its driving me crazy that I cant remember the title!
Its a female killer, and Columbo catches her because the film that she is controlling is not doing what it should be doing. It has something to do with a glimps at the screen when its time to change the tapes or something like that.."

Sounds to me like "Make Me a Perfect Murder", because they were actually in a pre-screening theatre (cinema?), where as Forgotten Lady was in her home.

So nice to see that I am not the only one who loves Columbo :)
Well, the episode I mean takes place at a cinema, not at home. The woman is actually in charge of changing tapes. The change is seen at the screen as a white spot, and the position of this spot (its not there, its too late, too soon or something)is what Columbo uses to frame the murderer.

It has something to do with the time she uses to kill the guy, its only a couple of minutes, then she is back at the controllingroom.

That definitely sounds like Make Me a Perfect Murder.