it looks like there is a skeleton dog somewhere on the level, and in this build it tries to drool ectoplasm. which is a gas, not a liquid. hence the crash.
p.s.: i haven't tested the save, just noticed that 12294 is the value of ECTOPLASM constant. and there was a test commit to make skeleton dog drool ectoplasm without actually converting ectoplasm to liquid. so the attempt to spill it crashes the game.
p.p.s.: easy to check, btw. start a new game, and go down the Attnam catacombs. there is a necromancer on the last level, and several skeleton dogs. if the game will crash with the same message, then i'm right.