The Might and Magic VI Patch
These are the patches available for the game:
The otherwise very useful patch 1.2 (which is an integral part of the Millennium Edition of MM6) unfortunately causes two bugs (while fixing a whole bunch of more serious ones). One dungeon the Shadow Guild in the Frozen Highlands won’t let you through its doors and a certain door in Castle Kriegspire likewise won’t open.
But if you are looking for a workaround, try checking out DaveO’s Angelfire page where you’ll find a copy of the MM6.exe file from the 1.1 version, look for the heading “Great support news for Millennium Edition users!”.
For Castle Kriegspire: Save your current game right where your party is facing the locked door. Quit the game, replace your MM6.exe file with the one you’ll find on those sites (remember to take a back-up copy of your own MM6.exe file first!). Start the game, load your save game, open the door, and walk to the other side of the now opened door. Save again, quit the game, now copy your own MM6.exe file back into the folder deleting the 1.1 file (you might want to confirm that you now have the 1.2 version back by right-clicking on the your MM6 icon and see, that it says version 1.2). Now load your new savegame and you’ll find yourself on the right side of the door which now is opened.
For the Shadow Guild in the Frozen Highlands: Essentially the same, except you need to make your initial save outside the dungeon, finish the whole dungeon using the 1.1 MM6.exe, and make your last save outside the dungeon again.
You’ll definitely want to return to the 1.2 version as it fixes some major bugs with the 1.1 version, it is very unfortunate that it also locks these doors.