error message

[zap]

That's a missing file error. First, look if the said file exists in the game folder, if it does , then it might be the case your computer was running out of RAM memory.

If it doesn't exist, something's gone awry.

I will be at my computer in a bit, I'll have a look too.

I should mention. This occurs in Artillery phase (mostly) stops the game and have to restart. You're right it only involves the Hungarians. A few times it has occurred firing infantry on infantry into those hexes. But the interesting thing is it appears to be only in certain hexes! Or maybe as you said Battle Cat it is something to do with the Hungarians.
Also it helps to know that several have played this scenario and no one so far that I know have complained about this occurrence.

I will try your suggestion Battle Cat