Medal of honour 2010 limited edition?

friends i have problem related medal of honor 2010 limited edition online key registration. I install medal of honor 2010 limited edition along multi player during installation i gave serial key n it install with multi player but when i run multi player mode and try to connect to server to join online then an error appear "not register from E.A" or something like this plz help me my friend i can't play multi player mod.