To reproduce:
1. Open project Unity355Test
2. Open TestScene
3. Attach MyUI script to an object
4. Run

or Drop this GUI into a scene to reproduce:

public class MyUI : MonoBehaviour {

public Vector2 scrollPosition = Vector2.zero;
void OnGUI() {
scrollPosition = GUI.BeginScrollView(
new Rect(0, 0, 200, 400),
scrollPosition,
new Rect(0, 0, 200, 300),
false,
true);

GUI.Button(new Rect(0, 0, 100, 20), "Top-left");
GUI.Button(new Rect(120, 0, 100, 20), "Top-right");
GUI.Button(new Rect(0, 180, 100, 20), "Bottom-left");
GUI.Button(new Rect(120, 180, 100, 20), "Bottom-right");

GUI.EndScrollView();
}
}