When installing the patch, a prompt to uninstall the game appears
When the game is patched, it scans the install folder to ensure all of the files are original and and present. If the patch detects that any files are missing or modified it will prompt to uninstall the game. This is an extension of the copy protection encoded into the patch.
The patch will only prompt to uninstall when applied if it finds a problem with the original installation of the game. If any of the original files are missing or modified then the patch will not install. To remedy the problem you will need to uninstall the game and delete any files left over in the in the installation folder (with the exception of the 'savegame'folder if you wish to keep your saved games). Restart the computer then reinstall the game making sure not to modify, overwrite or remove any of the original installation files. Now install the patch