ToME: the Tales of Maj'Eyal

If

Grand Corruptor is confused

and

you ally with him in the Demon Plane

then

The game freezes up

Sad! I was hoping to unlock that one...

Character Diviatax, level 29 anorithil, is the toon in question.

In beta20b ?
Can you grab the log for me please?

Yes, in 20b. The file was too large, so I cut the part after he went into the demon plane into 2 parts and attached them. Looks like an infinite loop of some sort where I can't dismiss the dialog box.