Bethesda Softworks has finally released a patch for Oblivion expansion Shivering Isles to fix the "FormID" bug that was ruining some people's games.
Those of you playing the game on PC can find the update on The Elder Scrolls website, whilst you thumb-twiddlers enjoying it on Xbox 360 can download the fix from Live.
You should also be aware that expansions bought using direct2drive aren't yet compatible with the patch, and those of you who installed beta Shivering Isles patches will need to reinstall the entire game.
The bug, which had already been patched to some extent on the PC, rendered the expansion unplayable on both formats after an extended period of time (between 50 and 120 hours on the PC, depending on your frame-rate, and between 75 and 150 hours on Xbox 360 depending on your play habits).
It has to do with the way the game identifies objects in the world. The simple version is that the game eventually runs out of identification numbers (formIDs) for things, confusing the way it manages system memory, corrupting data and failing to register objects when you save your progress.
Alternatively you can quest your way to our Shivering Isles review to see what we made of the game, bug or no bug.