Registration Problem

I bought Space Rangers 2 from Direct2drive.com and then saw the Reboot expansion here.  I bought the expansion and registered it, but it won't let me install the expansion because it says Space Rangers 2 is not registered.  I tried to add a registration with the code I received from Direct2drive.com, but it won't accept it because it didn't come from here.  I need to know what to do to install the expansion.  Thanks for the help!