How to select NIB for view controller in xcode4?

I have created a universal window based application in xcode 4. Additionally I created a FirstViewController class with a FirstViewController.xib file.

I dragged a Navigation Controller to the objects panel for the MainWindow_iPhone.xib. I want the root controller to be the FirstViewController so I selected it in the custom class property.

I now want the view to be loaded from FirstViewController.xib but I can't select it in the NIB name selector, it just is not listed there. When I type it in it says that it is not intended to be there.

The strange thing is that exactly this procedure worked for me in xcode 3.2.6

Any ideas?

"When I type it in it says that it is not intended to be there."

Hang on, isn't it the case that this is because: it is not intended to be there ..!?

There were many heinous problems in the ancient XCodes that could lead to a mess, XCode4 fortunately prevents said issues.

Just to be clear, FirstViewController is a subclass of what? There must be some problem, because it works fine.

We have had utterly no problem whatsoever dragging custom classes, into an xib, to have them instantiated, I just did a couple this minute to triple-check - no problem!!