Mount and Blade activation not working Thread

every itme i try to put the CD key into the activatiojn panle it accepts it, but after that instead of letting me play the full game it just brings the activation thing up again asking for my CD key. no matter how many times i have i have done it i cant put the CD key in. How can I fix it?

every time i put the cd key in it accepts it and thanks me for putting it in saying it has been activated. But it instead of letting me play the game makes me activate it again and again and again...