Since release of Overlord we have become aware of two critical issues which were not discovered during the extensive internal testing at Codemasters.
The first issue relates to the uninstaller for both the demo and the full game and applies if you installed the game to a custom directory. Anyone who installed to a custom directory should install this patch.
The other issue relates to a potential progress block late in the full game. If you are unable to apply the patch, this document will describe how to avoid triggering this blockage.

Workaround (for those who cannot patch)
There is no workaround once the bug has been triggered and saved, unless you have an Autosave slot with a save from an earlier part of the game.
However, you can avoid triggering the bug by:
1) When you find the first spoke have a minion pick it up, carry it to the wheel and attach it.
2) Only pick-up the second spoke if you have enough minions available (>12 in your horde, or in a Minion gate) to turn the wheel
3) When you have attached the second spoke, ensure that you turn the wheel fully before leaving the level.

If for some reason this is impossible (e.g. you have totally run out of minions) use the 'Change Autosave Slot' option in the pause menu at the start of The Brewery to keep the game progress up to this point stored in a different slot. The save game in this slot can be opened again later from the Load Game option in the main menu.
This use of 'Change Autosave Slot' is also a useful way to allow you save 'checkpoints' that you can return to at another time.

- Codemasters forum