I'll leave this report just in case.
2CD version.
A crash when trying to get back to Mortuary. I didn't try it "illegally" , so this is at least about normal dialogue way via one of the Dustmen guards.
Solution - start a new game, then load current game back. I thought this has to be about safe bif unpacking to cache from cbif (still leaves the question why the game handles it normally in the beginning and crashes when trying to do the same while I attempt to get back).
But this doesn't make much sense - starting location is AR0202.bif (2nd floor), while teleport location is AR0201.bif (1st floor). I checked - it doesn't unpack AR0201.bif too "just in case". Also there were no crashes at all while I were playing freshly started game - meaning safe needed transitions between all Mortuary floors and both ways out of the Mortuary too.
I do not know if this crash and/or "solution" happens/works all the time. For me it did as I recall.
My install is Fixpack -> UB -> Tweaks, running on WinXPsp3, if this matters at all.
Anyway, this is not critical as you see, I'm really just curious "What the hell happened?"©TNO in Tomb.