Error 72 seems to be the one that comes up with Gameguard thinks it's been tampered with.
The thing about gameguard, is that, while each game that uses it has it's own individual files, they're all used by a central program. If the files for installed games think they've been modified, then they can cause this error.
First thing I'd do, is delete the gameguard folders and gameguard.des files in ALL games you play that use gameguard. Gameguard's files are usually all updated at the same time for all games. It's possible that if some games haven't been updated as fully, it'll think you're trying to trick it with an older set of files.
Next, make sure none of the programs from the following list are installed. Even being installed can cause gameguard to refuse to run, even if not running.
NProtect GameGuard - Wikipedia, the free encyclopedia
I'm trying to find a method for actually removing gameguard so it will fully reinstall itself clean. I know it has files in the system folders for windows, as I've come across them before while working, but I can't find them now.
Ok, here's a program that's supposed to remove it entirely. If none of the above works, try downloading the program here, running it, reboot, and then try to run GC again. I've read through the source code, and all it's doing is stopping services, and deleting related files and registry keys, so it should be safe. Make sure to back up first though in any case, as you should any time you manipulate your registry.