The name 'GameObject' does not denote a valid type ('not found'). BCE0018

I edited my script in MonoDevelop-Unity and I am trying to debug it. I am getting error while creating objects: The name 'GameObject' does not denote a valid type ('not found'). BCE0018

Code:

 var e2 : GameObject = GameObject.CreatePrimitive(PrimitiveType.Sphere);
 e2.transform.position = Vector3(2, 1.5, 0);

I noticed that many people have similar error because of misspelling, I can't see any, I did everything according to tutorial http://docs.unity3d.com/ScriptReference/GameObject.CreatePrimitive.html I tried retyping, it does not change anything.

In main Unity window I am getting error few lines before with StreamReader

 sr = new StreamReader(txtname);

and many variables (unknown identifier) but not with GameObject. Should I care about MonoDevelop?