Install Impulse from http://www.impulsedriven.com, log in with your forum account. Click the Impulse icon in the top left and select "Register a product". Put in your Sins serial, and you will be able to download and install the game (it will show up in the My Games) tab. No cd required, and it'll work just fine

You can try emailing [email protected] with a screenshot of the error you're getting, but they won't answer until Monday or Tuesday since they're off for the weekend, and usually downloading from Impulse is the first suggestion that gets thrown out