and then the new update breaks the application

I download the european version of the patch. Bleugh, another 200MB download. I apply the patch and now the game no longer works as it claims the game DVD is incorrect. Piece of s**t. There’s no way to unpatch the program so I uninstall it to reinstall it. I forgot to have the game manual handy. Hunt the install key.
Could it be that having Splinter Cell and F.E.A.R. installed on the computer at the same time could be causing problems? Or was it an incorrect patch, as it worked before I applied the patch.
Annoying, I’ll just have to stick to playing Splinter Cell until I’m finished it.