Display GUI and screen lock and show cursor when OnTriggerEnter (Auto NPC menu enabled)

My situation: Trying to show some specific form options as soon as the the player reaches the counter. As soon as the player exits the counter area, the form options disappear.

My approach: I used OnTriggerEnter, show GUI. OnTriggerExit, show GUI is false. In the GUI shows 3 buttons. Each one displays a texture (a form image). In the near future, I wanna add a video instead of an image/texture (which I’m still trying to figure out). At the moment, I’m focusing on displaying forms upon button click (e.g. if Form 1 button is selected, Form 1 texture displays. If Form 2 button is selected, Form 2 texture displays.)

My problem: But at the moment, when the player tries to click on the form button, the screen moves to it and no cursor will show. Upon clicking the form button, no GUI Texture will show. Here’s my code:

private var showCounterMenu : boolean = false;
var Form1 : Texture;
var Form2 : Texture;
var Form3 : Texture;


function OnTriggerEnter(other : Collider)
{
showCounterMenu = true;
}

function OnTriggerExit(other : Collider)
{
showCounterMenu = false;
}

function OnGUI()
{
 if(showCounterMenu == true)
 {
  GUI.Box(Rect(10,10,100,100),"Counter Menu");
  if(GUI.Button(Rect(20,20,100,100),"Form 1"))
   {
    GUI.Texture(Rect(Screen.width/2 -100, Screen.height/2 + 200, Form1.width, Form1.height);
   }
  if(GUI.Button(Rect(20,20,100,100),"Form 2"))
   {
    GUI.Texture(Rect(Screen.width/2 -100, Screen.height/2 + 200, Form2.width, Form2.height);
   }
  if(GUI.Button(Rect(20,20,100,100),"Form 3"))
   {
    GUI.Texture(Rect(Screen.width/2 -100, Screen.height/2 + 200, Form3.width, Form3.height);
   }
 }
}

What do I do? I get this error where it says something about too many GUI Clippings.

Screen.lockCursor = true;
Screen.showCursor = false;

function OnTriggerEnter(other : Collider)
{
Screen.lockCursor = false;
Screen.showCursor = true;
}

function OnTriggerExit(other : Collider)
{
Screen.lockCursor = true;
Screen.showCursor = false

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;
}