This is my story. I was polishing the campaign map for Iberia Total War.
I modified map_heights and also some port points in map_regions.
Everything looked ok, as can be seen in those screenshots:

The coast is now better, with less "steps".
I was testing the campaign. Everything run ok up to the first battle. I fought it and when the game returns to the campaign map:

The map had disappeared and everything was BLACK!
I can follow the campaign, in fact a blind campaign.
If I start a new campaign, the map remains black (map.rwm?).
If I delete map.rwm and I charge the old black campaign, everything is ok. So it seems there is some problem when charging map.rwm after a battle.

I had modified the temples, and I supposed that the modification in descr_settlement_plan was responsible for this problem (as it was after a siege). But it happens also after a battle in the open land.

Any ideas?