Can you post a screenshot of your model in shaded mode with the arm selected.

thanks

Edit: Do a screenshot of all 4 views (front, back, side, top). You know, all four panes showing at once. Just zoom into the intersection in all four views so we can see it a little better. don't need to see the whole model in each view, just a close up of where the two pieces intersect. Just make sure that you have the arm selected (highlighted) or that you are in shaded mode with wireframe on.