Interface Builder Inspector - always shows (Empty Selection)

I have been using Xcode and Interface Builder now for several weeks. When building a view with Intervace Builder I have always been able to drag objects from the library to the view and then change attributes with the inspector. Now for some reason that I cannot figure out, the inspector is always displaying (Empty Selection) no matter what library object I have selected. I have Xcode 3.1.4 and have just created a new project for a tutorial, however none of the views that I already have created work either.
Any ideas?