motionblur not work on my android phone(android/ios)

I use motionblur in my game,it works perfectlly on my pc,but not work on my android phone(moto defy and htc Desire HD),with my trace,I am sure my devices are both support RenderTextures,but in the ‘MotionBlur.cs’,the function of ‘OnRenderImage’ not work! as the follow:
void OnRenderImage (RenderTexture source, RenderTexture destination)
{
Debug.Log(“01”);

}

the ‘01’ not trace all the time.

btw:my license is unity pro,android pro,iphone pro.

thanks in advance!

close the question.

the phone not support image effect,what a pity!