Hi Pharan, thanks for your reply.
Yes I tried pressing "Auto" but to no avail. Actually my process was to put bones first, then create mesh, then that's the only the time I bind everything to the bones.
Maybe the mesh that I've made is the culprit?
Hey Guys,
Just an update, I think Pharan you're correct about the mesh having the problem. I tried redoing the mesh and it worked! 🙂

Thanks for your help specially Pharan. More power guys!