Kev999
Also check your downloads page. It's possible that you might have more than one copy of Rapture.
I just loaded up a new machine, and if you have multiple copies of Rapture (or Dimension Pro) in your account due to Producer/Platinum purchases, you will also have multiple codes, but only one set will work.
As mentioned above, it is easiest to run the standalone (in C:\Program Files\Cakewalk\Vstplugins\Rapture) as administrator and try each of the codes in your account until you hit the one that is accepted.