In Xcode 5.1 - there is a self help area that did the job for me.
You'll find it in the General section after clicking on your project name under > Targets. You should see a warning icon and a description of the issue in the Identity section (right where you type in your build/version numbers).
It noticed that there was no certificate currently stored and via some self-help boxes and a change of my password, I got it going.