I was having problems with getting depth frames (notably, when NOT using grabLabel).
I managed to fix it by changing line 395 of ofxKinectNui::update from:
depthbit = depth(depth.Width() - x, y);
depthbit = depth(depth.Width() - x, y) >> 3;
Sorry for this late because of my pc was crashed. : (
I will update ASAP!!