I always found that on my computer, there were places in MM6 in which certain actions tended to crash the game. I learnt always to keep a range of backup savegames as a precaution against this.
For example, when I was playing MM6 years ago, I was in a corner of one of the big rooms in Kriegspire Castle. I turned clockwise to leave the corner, and the game crashed. Fortunately, I had a very recent save, so I restored the game and tried it again, and got the same result. But I found I could turn anticlockwise quite safely. I never found out why, and I never had the problem in any other game. Total mystery to me!