Delayed/stuttering/transposed playback sound

Hey,
I just downloaded mscz 4, when i want to listen to my piece it is not smooth at all. It sometimes transposes the music up by one step, stutters for a few bars (repeating notes when they are not there), the tempo isn't right...
It is an old mscz 3.6 - file, does it have anything to do with that? (if so, how do i update the file?)
I hope one of you can help me to enjoy the new sounds!
Thanks in advance,
Thijs