I\'ve just enrolled in Apple\'s iOS Developer Program (account type: Individual).
In my Xcode organizer on my iPhone 4 device I click \"Add device to provisioning portal
I'm getting the same issue in Xcode. I think it's related to the wildcard app ID that Xcode creates for you. There seems to be an issue with that process that then cancels the device addition process that you're trying to complete.
You should still be able to add the device via the iOS Dev Center. Once logged in, go to the Provisioning Portal and you can add the device there.
Not perfect I know, but should allow you to start building apps and testing on your device until the Xcode issue is resolved.