Setting a guiTexture to Null

You probably need to destroy it.

GUITexture is a component therefor you need to destroy it and then you may set null to the variable if you wish.

For instance, if I had a script residing on the same GameObject that I had the GUITexture I no longer need, I would call the following:

 Destroy(GetComponent.<GUITexture>());

or if I already had the reference to the GUITexture:

 var myGuiTexReference : GUITexture = GetComponent.<GUITexture>();
 
 Destroy(myGuiTexReference);
 
 myGuiTexReference  = null;