I used the eval() function on web player

In aim to make an unity3d webtutorial for beginners, I wanted to evaluate user-code, written in an GUI-textfield, executed by Button.

 var userInput = "cube.transform.position.x = 1;" //just for testing
 
 var cube : GameObject;
 
 function Start(){
    cube = GameObject.FindGameObjectWithTag("Finish");
 }
 
 function ExecuteButton(){
    eval(userinput);
 }
 

It worked fine on my local machine, but the web-player crashes each time. Anyone has an solution for me?