You will have to do a fresh clean install first though.What I mean is uninstall the game,delete the dir. file in my programs and do fresh install of the game.When done you can then install the 2552 patch do not reinstall the 2501G patch that is an old one and your game will be out of date.This is the same with mine I have to do the same a clean install my is out of date I still have 2501g patch in it.
I hope you understand what I am trying to say a fresh clean install is like you are installing it for the first time that you just toook it out of the box.
Just trying to help and don't let name fool you and I hope it does help