Now I'm pi**ed!
Like others, I've had a few random lockups throughout the game, but have always been able to progress after restarting from where I left off............until now. No matter what I do, the game crashes when I try to reach the chandelier with the "long pole" in Gideon's gallery. I've tried going at the chandelier from every angle, running the game as an administrator, etc. Unlike others, I've never had any problems with audio so I don't think it's connected with my RealTek High Definition (on-board) Audio.
I'm running Vista Home Premium 64 bit on a gamers machine using an NVidia GeForce 9800 GT card and the aforementioned on-board audio.
Any ideas?

That worked! Thanks for the solution!!

I am starting to wonder how much research GOG are doing on the games before they release them. They say they are running them first but I can't see they have done that, it's common knowledge that the midi has to be muted. Unless the player had changed the settings not knowingly.

Well that's not being fair to GOG in this case. MIDI audio IS muted by default in the GOG version of Overseer. You can activate it in the options but it's at your own risk because indeed it's a known fact that MIDI crashes the game in some places (the chandelier being one of them).

as I posted above , if the player changed the setting without knowing why the midi is muted.