This isn't a problem for me any more, I don't know how I solved it (I restarted AGS and that didn't fix it, I also tried reloading the room, that didn't either... ) But I would sure as hell love to know why it happened.
I had a scrolling screen with a 256 colour BG. Everything was working fine and I had the areas all set. I had tested the room before, with MUSIC2 playing. Then I changed the music to MUSIC3 and tested it again.
It seemed fine, except for an odd sound when it loaded the room, like a piano key was stuck or something. If you tried to walk it would also be fine. It was only WHEN YOU WALKED ON A CERTAIN AREA of the screen that it crashed with an error and quit AGS. Every single time the same area. Eventually I dismissed it and kept working, telling myself I'd ask here later. I imported an updated version of the same background and tested it, forgetting the problem... which was gone.
What the heck was that? It seemed as though the Music and the Background disliked each other or something! And why would a midi make it crash in one particular area of the room?
I'm a very curious person ;D
Maybe there was a region area with a breaking script assigned to.
No, it only occured when THAT midi was playing, and it only happened on THAT area of the screen. The midi played fine, as I said, except for a weird Pianoish CLUNK at the start, which isn't in the actual midi. It really was bizarre. And it stopped happened after I reimported the background, even though I didn't update the areas or anything ???
strange... haven't you saved a copy of game with that bug still in?
Didn't occur to me, it was only when it was gone that I realised it wasn't something I'd done wrong, maybe. :-\