Playing MKV with GOM player

I am using GOM player now for over a year and I never had any problems with it. Now, since a few weeks it can't play the new encoded .mkv files. The strange thing is that it still plays MKV's I downloaded a while ago.

When I try to play such a 'new encoded MKV file' I get the message: Can't use overlay mixer.

I have the same problem on my other computers.

I can still watch the MKV files with VLC, Windows Media Player Classic ... but not with GOM.

Someone has the same issue or knows how to solve this problem?