AntisheilaPower, Nephryrinn, deepke, AndrewC: Please wait until "Server Load" under "Service Status" in your cPanel is below 4, and then try adding the domain again once. You will have to wait 24 hours after adding your domain for it to become active.
Let me be clear: if you don't wait for the server load to be below 4, adding your domain will not work and you will come back here and whine about it and it'll piss us both off. Follow my instructions carefully.