Differences between @+id/foo and @android:id/foo syntaxes in main.xml

@+id/foo means you are creating an id named foo in the namespace of your application. You can refer to it using @id/foo.

@android:id/foo means you are referring to an id defined in the android namespace.
This namespace is the namespace of the framework. In this case, you need to use @android:id/list and @android:id/empty because these are the id the framework expects to find (the framework knows only about the ids in the android namespace.)

http://groups.google.com/group/android-developers/browse_thread/thread/dc8023b221351aa7?pli=1