This is using win32-notiles.
Screenshot at the time of crash
Save file state at the time of the crash
In case it matters... my last action was to cast Throw Frost.
Oh and the sheep probably fell in the water as a result of confusion from a previous Mephitic Cloud.
I was able to reproduce this problem by restarting from the attached save. I cast Mephitic Cloud into the herds of sheep until it crashed again. Sometimes the sheep will drown and it does not crash in that case.