Window already open bug

[Pepin Martel]

I'm new to computer wargames of this type, but as a student of the Great War I'm really happy with this game, except for one big problem. I keep getting an error message deep in each scenario. Something to the effect of "This window is already open", and that's the end of the game.
surely this isn't the end of the game. Any advice. Pretty computer illiterate here, I downloaded the game from a purchased disk.
Thanks