I have
the exact same error and this can be easily reproduced by using WindowBuilder Pro within eclipse and creating a new class:
WindowsBuilder -> Swing Designer -> Application Window.
When attempting to Run or Debug the application from inside eclipse, the window is created and the same error messages as the OP are written to the console, but the application doesn't appear to complete initialisation; it just sits there with no menu bar and it's necessary to 'stop' the application from within eclipse.
If I run it from the command prompt however it works fine. Weird.
Any help would be appreciated.
My system: Mac OS 10.6.6, Eclipse 3.6.1 (Helios)
Java(TM) SE Runtime Environment (build 1.6.0_22-b04-307-10M3261)
Java HotSpot(TM) 64-Bit Server VM (build 17.1-b03-307, mixed mode)
Here is the code: