ToME: the Tales of Maj'Eyal

Encountered this when trying to exit the Arena and return to Derth - this occurred twice with two Alchemist characters (having reinstalled Tales for the second one) but a subsequent playthrough with an Adventurer worked OK so could be class specific.

First error message is contained in the file starting 125....

When acknowledged, second error message (file starting a45...) appeared. Acknowledging this resulted in a blank screen until the mouse was moved and then the error message would re-appear. This continued indefinitely.

Using the GOG version of Tales of Maj'Eyal with all 3 expansions. No mods added initially, but did add the Adjustable Levelup on the second run (just to increase the level/attribute caps to 1,000) which didn't seem to change anything.