OK, there is another (and much more daunting possibility) it the vertexes for the "spacerbone" and "hip" don't line up EXACTLY it won't weld. It may be that something got moved a tiny bit after the model was divided. This will prevent the weld from working. Unfortunatelt this means you will need to venture back into the modeler, weld that seam back together and try dividing it again. Be extremely careful not to move any parts any where along the process.