The obvious answer with your hardware : Try without anything Matrox installed.
Apparently it has been working perfectly with all the current configuration, so I doubt that it is a Matrox issue.
If you use cineform codecs you might have issues with a current release. There is apparently some issues with SDK (at least as far as cineform is concerned) that might affect RealTIme rendering engines. Who knows, matrox may be affected too.
I've noticed the same issue when I 'upgraded' my GPU from GTS250 to GTX260 (a move I regret).
Now, I'm about to upgrade to GTX470 and I hope this annoying and uncontrolled playback stopping will go away.
Anyways, please post a solution for this problem if you find the culprit.
My specs are:
5 dedicated HDD
please post a solution for this problem if you find the culprit.
I fixed it by following the instructions from Todd's link. Although the instructions are for Mac users I just did exactly what it says and I got it playing back my multicam sequence without stopping.
Here is what I did, I created an admin account because my workstation has only got one user account, then I created a new project in that user account with the same sequence settings. I then imported the whole project which was not playing correctly and waited for it to load and conform all files. After that I started playing and cutting my multicam sequence and it played for 30 minutes without stopping. Following this I returned to my main account and started editing the project and it played back without stopping at all.
So seems to be fixed for now. Good luck with yours.