I'm pretty new to blender so currently I'm in a pickle. When I first finished the model and had the arm attached I noticed that when I shaded it smooth it didn't look right. I figured I attached it wrong and deleted the arm and attached an exact replica of the left arm to the body. The problem seemed to persist and it seemed to also effect the texture, despite the arm being joined with the body and UV editing showing it clearly as part of the mesh. I colored it to show some of the problem, the whole texture paint is purple except the arm. 
I have done some research but without exactly knowing what's wrong with, whatever I did wrong, it's difficult to find answers. If it helps anymore I have the version that was shaded smooth, adding subdivision surfaces doesn't help. It seems to be separated even though it is joined to the body, the other arm is fine.
Help would be very much appreciated!