I see what you're doing. If you use the views that are off of the View->Other->camera01, camera02, etc., all of the geometry is shown just like the Front, Perspective, etc. windows. By defult the cameras and lights are shown. This is not the same as the View->Camera view which automatically hides cameras and lights. So your render has the camera in the picture which is why the funny square is visible - that's the camera's lense shade. Turn off the camera and lights (click the camera button on the left-hand toolbar) and it should work.
However your file showed a couple of related probelms:
1) The ART renderer can crash when there is a mesh with no points in it. Your model's mesh01 is like that. I've fixed Anim8or but you need to delete mesh01if you want to render using ART. Bug #097-007
2) Shadows are disabled when you turn them off in the View->Preferences dialog for the ART renderer. But they seem to be ignoring the light's shadow setting now. I'll fix that. Bug #097-008