"This computer is not running genuine Windows" error

Installed the RC with a key from a blog as I lost my first key when I downloaded it.

I keep getting an error saying "This computer is not running genuine Windows" in the control panel and I can't activate Windows 7.

I am not trying to pirate anything, I just want to test out the RC before I buy Windows 7. Have I done something wrong during the install process?

Try restarting the Software Protection service.

Ok, you said you used the key from a blog.
What MS have done is they issue these keys to people who download it. Someone somewhere has probably used that key already, and that is why it is coming up.
Just obtain a new key from MS, simple eh!