GUI.Button doesn't show texture

Hi,

in my project I've one GUI.Button and ten GUI.RepeatButton. At each button is assigned a Rect and a Texture.

All buttons are made in this way:

 var resetAll : Texture;
 var zoomIn : Texture;
 var zoomOut : Texture;
 var rotateRight : Texture;
 var rotateLeft : Texture;
 var rotateUp : Texture;
 var rotateDown : Texture;
 var rotateUpRight : Texture;
 var rotateDownRight : Texture;
 var rotateUpLeft : Texture;
 var rotateDownLeft : Texture;
 
     if(GUI.Button(new Rect(526,38,32,32), resetAll)) {
     }
     if(GUI.RepeatButton(new Rect(458,4,32,32),zoomIn)) {
     }
     if(GUI.RepeatButton(new Rect(458,72,32,32),zoomOut)) {
     }    
     if(GUI.RepeatButton(new Rect(560,4,32,32),rotateUpRight)) {
     }
     if(GUI.RepeatButton(new Rect(560,72,32,32),rotateDownRight)) {
     }    
     if(GUI.RepeatButton(new Rect(492,4,32,32),rotateUpLeft)) {
     }
     if(GUI.RepeatButton(new Rect(492,72,32,32),rotateDownLeft)) {
     }    
     if(GUI.RepeatButton(new Rect(560,38,32,32),rotateRight)) {
     }
     if(GUI.RepeatButton(new Rect(526,4,32,32), rotateUp)) {
     }
     if(GUI.RepeatButton(new Rect(526,72,32,32),rotateDown)) {
     }
     if(GUI.RepeatButton(new Rect(492,38,32,32),rotateLeft)) {
     }

The buttons are displayed and they works fine but no texture is showed in each button.

I've assigned textures (32x32 px PNG format) via Inspector with Drag and Drop.

How can i solve this issue?

Thanks in advance.