That is most likely to be the SweetFX shader package I included with Patch #2, a few other members have also had problems. Go to the Medieval II Total War folder in the Patch and you will see the ‘mods’ folder and a bunch of files + a SweetFX folder, they are all to do with SweetFX. Go to your Medieval II Total War folder and delete that SweetFX folder and files from your install. That should fix the problem.