Playing a ME Wizard and got the following message when descending from UD:1 to UD:2. I hit > to go down the stairs and before the UD:2 loaded I received:

*** A serious internal error has occured.
*** PLease report the following message at 'http://adom.de/bugs' and describe what you did when it hapend
Putting a monster (royal guardian, 57) at a blocked place (27, 16) [1] {9, 2}.
*** This still could ruin your game though ;-(
You sense immiment danger...
There is a stair leading upwards here.

In UD:2 I found myself in a 3x5 room with a dire wolf and a single herb patch.

I have a savegame I can attach if needed.