Why Is OnMouse Not Working Correctly?

Sorry for the generic always asked question, but my OnMouse isn't working correctly. On all the tutorials I've seen, when the person hovers over their GUI Textures, their script allows their textures to light up indicating that they're over it. But when I do it, it worked for most of the GUI Textures, but not all. If I remember correctly there are about two that don't work. One won't let me hover/click it at all, and another won't let me click it unless I go to the bottom of the screen, then it shows up. So what could be the problem? Are the GUI Textues too close to each other, or something else? Here's my script so I don't look crazy:

 public class Click : MonoBehaviour {
 
     public Texture2D normalTex;
     public Texture2D hoverTex;
     
     
     void OnMouseEnter(){
         
         guiTexture.texture = hoverTex;
         
     }
     
     void OnMouseExit(){
         
         guiTexture.texture = normalTex;
         
     }
     
     void OnMouseDown(){
         AudioManager.AudioInstance.PlaySound ("Sound");
         Application.LoadLevel("Scene1");
         
     }
 }

It's the script for the one that actually let's me click it, the other button has the same script except a different scene loader. Here is how my GUI Textures are arranged:

This is the one that I have to go all the way to the end of the bottom part of the screen(wow that was a lot of "the"). So it let's me click it, but not right on it. The other GUI texture that doesn't let me click on it uses the same structure. So what can I do? By they way I use OnMouse because I'm developing my game for IOS Ipad/Ipod touch.