How do I workaround this new warning in Xcode 4.3.1: "Scene is unreachable due to lack of entry points..."?
You can just set an identifier. In Xcode >5 on the identity inspector on the right pane, you'll find a field called "Storyboard ID". Put any string in there, and Xcode will be happy again.
It just wants to know you could reach it (via that identifier) if you wanted to.
In newer versions of Xcode: Just set a title in Title in the Attributes Inspector and then set an identifier in the Storyboard ID in the Identity Inspector of your controller.
You may have accidentally copied and pasted a view controller on top of the real one.
Try dragging the offending view to see if there's anything underneath.