Getting crash on disable of 3d object

Hi, I am stuck over very strange problem, I have downloaded 3d object in .fbx format which is actually superman and I have loaded this onto scene not from code. I want to hide this object on specific action and doing following to hide but my app gets crash.

GameObject.Find("SuperMan").active=false;

This object is in scene I don't know why this happen, kindly help me on that. This will be great for me. Thanks in advance.