NGUI 3.4.9 error NullReferenceException UnityEngine.Material..ctor (UnityEngine.Shader shader) UIDrawCall.CreateMaterial ()

Editor is showing me NullReferenceException UnityEngine.Material..ctor (UnityEngine.Shader shader) UIDrawCall.CreateMaterial () again and again. I am using NGUI 3.4.9 paid version.

If I use

 var texture =  www.texture;

It shows me error. and if I use

 var texture =new Texture2D(1,1); It is working fine.

I need to fetch image from url thats why I am using www. But if I fetch image from my resources then it is working fine. I was using previous version of NGUI(free) and the code was working impeccably and great. After when I updated my NGUI folder (package) with new one from that moment get this error again and again.

I guess it is not www kind of thing It is some NGUI rendering bug. But why it is occurring only with www.texture

Please guys help me out of this.