unknown terrain

[dabber]

I haven't played in two months, and now it doesn't work. I don't think I changed any code in that time, but probably I broke the code inside my version of Legend of the Invincibles II. I am hoping someone can give me a pointer to what might be wrong. This add on campaign, starting it from scratch or loading a save file, produces some version of a terrain error - "unknown tile in map". What terrain code it cites varies with the scenario, but the fatal error "unknown tile in map" is constant.
The map files are unchanged
terrain.cfg is unchanged
_main.cfg is unchanged

What might it be accessing incorrectly?

[Ravana]

Locate which terrain code is affected, and then look where it should be defined.

[dabber]

I've seen at least 5 different terrain codes reported as in error. All appear correct in terrain.cfg.