Why won't new class show up in Identity Inspector/Custom Class in Interface Builder?

I'm having a repeating problem in Xcode 4.5 and would like to ask for help/advice.

Have been creating a new class, BIDSwitchViewController, which is a subclass of UIViewController. When I go to the Identity Inspector to layout the .xib file, of course I want to change the class it belongs to to BIDSwitchViewController, so that I can layout my objects and make my connections.

But BIDSwitchViewController doesn't show up in the dropdown list for Custom Class in Identity Inspector. So then I hardcode "BIDSwitchViewController" into the text box, but then that doesn't stick.

What am I doing wrong,and what can I do to fix this?

Thanks in advance.