I don't see anything suspicious in errorlog.txt, but here are the last few entries. I'm guessing entries at the bottom of the file with higher ##s are newer:
#37798:Path Goal Seek Item for Storage:Station Mill Building at 16,190,19
loop path fail: <same square> dwarf,Store Item in Stockpile,263,68,17 -> 102,176,22: Id #25478:Path Goal Seek Item for Storage:Station Mill Building at 260,94,17
loop path fail: <same square> dwarf,Dump Item,264,102,17 -> 259,60,17: Id #26369:Path Goal Seek Item for Storage:Station Milling Flood at 260,90,17
loop path fail: <same square> dwarf,270,97,14 -> 280,107,12: Id #26371:Path Goal Seek Station:Station Mill Building at 279,107,12
loop path fail: <same square> dwarf,Store Item in Stockpile,36,243,16 -> 37,209,10: Id #38133:Path Goal Seek Item for Storage:Station Mill Building at 53,226,14
loop path fail: <same square> dwarf,29,226,16 -> 34,226,16: Id #38245:Path Goal Seek Station:Station Mill Building at 33,227,16
loop path fail: <same square> horse,27,243,16 -> 34,245,15: Id #40787:Path Goal Seek Station:Station Owner at 71,245,15
loop path fail: <same square> dwarf,Dump Item,31,243,16 -> 16,167,16: Id #39678:Path Goal Seek Item for Storage:Station Mill Building at 15,191,19
loop path fail: <same square> dwarf,Store Item in Bag,36,243,16 -> 4,238,16: Id #37469:Path Goal Seek Item for Storage:Station Mill Building at 34,230,16
loop path fail: <same square> dwarf,Dump Item,16,191,16 -> 26,171,16: Id #37719:Path Goal Seek Item for Storage:Station Mill Building at 20,180,19
Maybe someone can find a fix for this that I've missed. I can live without the king, but I was still having fun in that fort. Was preparing to breach the HFS. I've considered playing through the couple of days until migrants in 40d16, then reverting to 40d if possible to keep playing. I just haven't done it on the off-chance that I've missed the obvious fix that will let me get the King.
Edit: I've also now done a fresh install of 40d, changing only the cat bug so it'd run, and I still get a crash.
Some other notes: I'm playing with Temperature, Weather, and Economy off for framerate boosts. That explains my, um, unconventional fortress design of wooden bins and barrels all around the magma pipe. If you start it up without temperature off, things become !!things!! pretty quickly from fire snakes.