Used game won't work.

[SquireM]

I bought C&C 4 off of Ebay. When I try to play it, I get a message that the registration code is already used. Is there a way to reset this? Failing that, is there a way around it. For the moment, I'm not interested in playing with others online. Is there a way I can just play the campaigns and not have to log on every time?
Thanks

[=LEVIATHEN=]

You may want to contact the person you bought it from. They may or may not have uninstalled the game, and that would be the problem.