Steam....yes. Steam has mucked up things royally for RS. In frustration I copied an entire working RSIII 'data' directory into my Steam copy of RTW. I disabled ANYTHING that would mess with the install by checking it or 'updating' it. Tried to run RSIII, can get into the game, run Custom Battles, got to the screen where you can choose a faction to play, chose Rome, clicked start, the map tried to load, and then crash.
I have watched the map load for so many years that I can tell, within a good guess anyway, where the map is crashing in descr_strat.txt, and why. The 'why' in this case seems to be when the game tries to load the 'Boii' as a faction. It is at about that spot in descr_strat that it crashes. It also crashes there even when I modfolder RS......so what this tells me is that Steam has done something that IMHO is patently illegal...they have 'changed the way the game works'. I've read a ton of times, CA reps saying that you can change RTW any way you want, as long as 'you don't change the way the game works'. Well, RSIII works fine on ANY version of RTW\BI\Alex EXCEPT ^&%$#@! Steam!! And this really pisses me off.