Long story short:  I bought Demigod the other day and was installing it via impulse when I was reminded that I could install SINS over Impulse as well because it was already showing up on my games page (I had always installed it from cd before).  After installing demigod I tried installing SINS too and it refused to validate my key.  I played it before, registered before, patched before etc but impulse refuses to let me.

My key shows up as legitimate and registered on my account page as well as in emails regarding my account, I've doubled checked the impulse key is the same as the one in my account and everything matches up.  I'm at a loss, just keeps repeating "Error: the serial number you have entered is not recognized by impulse..." whenever I try to install.

Edit:  It is the collectors edition, if that makes any difference.