Unity iPhone crashed in ShaderLabs

Unity iPhone crashed in ShaderLabs. I doubt that it may be caused by changing RenderQueue of my GameObject. (Since it crashed after the modification of that part of scripts.)

Here is the call stack to trace:

 0    0x0111047c in ShaderLab::Pass::ApplyPass(ShaderLab::PropertySheet const*) ()
 1    0x0114b950 in Shader::SetPass(int, int, ShaderLab::PropertySheet const*) ()
 2    0x010e2d30 in Unity::Material::SetPassWithShader(int, Shader*, int) ()
 3    0x011bfccc in ForwardShaderRenderLoop::PerformRendering(Light*, RenderTexture*, bool) ()
 4    0x011b3dbc in DoRenderLoop(Camera&, RenderLoop&, RenderingPath, std::vector<SceneSlot*, std::allocator<SceneSlot*> >&, bool) ()
 5    0x0105db5c in Camera::DoRender(void (*)(Camera&, RenderLoop&, std::vector<SceneSlot*, std::allocator<SceneSlot*> >&, Shader*, std::string const&), bool, Shader*, std::string const&) ()
 6    0x0105e540 in Camera::Render(int, Shader*, std::string const&) ()
 7    0x0113bfec in RenderManager::RenderCameras() ()
 8    0x0111ec18 in PlayerLoop(bool, bool) ()
 9    0x01179a90 in UnityPlayerLoop() ()

And the following is the changes of my codes:

 t_Prefab2= msupportclass.GameObject_ADD_Prefab_localScale(
                 t1,
                 "score_number_"+ a1.ToString(),
                 new Vector3( i_x,  i_y, 0),
                 new Vector3( 90, 180, 0),
                 new Vector3( 0.15f, 0.15f, 0.15f));
 // The following 2 lines were newly added and the program starts crashing
 if( t_Prefab2!= null)
     t_Prefab2.renderer.material.renderQueue= RenderQueue.Overlay;

Any ideas please?

P.S. it only crashes in iPhone/iPad and never in the Editor