Problem with using offset for scrolling screen

I have been using this script for a scrolling screen for awhile. It used to work perfectly. But for the past 2 weeks, suddenly the offset failed to work properly. And I don't have any idea on how to fix it.

Please tell me what is wrong. Thank you all very much.

 #pragma strict
 
 var Speed : float = 0f;
 
 private var scroll : boolean = true;
 private var _mod : float = 0f;
 private var _modStep : float = 0.005f;
 private var _textureWidth : float;
 
 function Start () {
     _textureWidth = gameObject.transform.localScale.x;
 }
 
 function FixedUpdate () {
     //Debug.Log(scroll);
     if (scroll) {
         renderer.material.mainTextureOffset = new Vector2((_mod * Speed)%1, 0f);
         _mod = _mod + _modStep;
         if (_mod > _textureWidth) _mod = 0;
     }
     
 }

The script is credited to Mike Geig. I only take it from his video.

And the problem is this: https://www.dropbox.com/s/yihh5mdb34opuzt/offsetproblem.jpg