Yesterday it happened again after it was running for about 2-3 hours on a colossal custom map,

I do not run the program as administrator, even though the GOG installer turns this on for the executable.

It is like the game freezes and you cannot interact with the menus, a new window opens on the desktop with the error Access Violation.
If you use Alt+Tab to switch between application and confirm the error, you actual get the ingame controls back. Unfortunately all the Text is gone from the windows and you do not know what you are clicking at :)

This only leaves the good old task manager to close the program.

//edit: on a large map, the computer turns do not take as long and I didn't get any error yesterday. Must be some limit it hit or something...

If computers were like wives, that would be the one error that would NEVER happen

I also had that error recently, but the text was fine for me and I could continue playing the game after alt-tabbing back. The new update seems to have caused this. I hope it will not break the campaign later on.