User blog comment:Mathmagician/Installing Reborn Mod - Walkthrough/@comment-173.63.247.160-20120319001019/@comment-4674838-20120319002217

Do you have a 64-bit Windows operating system? If you're using 32-bit -- go to your control panel to check -- then Reborn won't work and you'll probably get the error message about the game not being legitimate, even if it is. Also, if Steam isn't "Run as administrator" you can get the message about "Launch the game through your Steam client" even when you are launching through Steam. Those are the only 2 error messages that I know about specifically. I don't know if there's any issue relating to Steam being installed on D:\ instead of C:\