Ambigous reference in GUIContent

first error:

Assets/6by7/ProGrids/Scripts/Editor/ProGrids_GUI.js(108,56): BCE0004: Ambiguous reference ‘constructor’: UnityEngine.GUIContent.constructor(UnityEngine.Texture, String), UnityEngi

Second error:

Assets/6by7/ProGrids/Scripts/Editor/ProGrids_GUI.js(114,55): BCE0004: Ambiguous reference ‘constructor’: UnityEngine.GUIContent.constructor(UnityEngine.Texture, String), UnityEngine.GUIContent.constructor(String, String).

Third error:

Assets/6by7/ProGrids/Scripts/Editor/ProGrids_GUI.js(120,55): BCE0004: Ambiguous reference ‘constructor’: UnityEngine.GUIContent.constructor(UnityEngine.Texture, String), UnityEngine.GUIContent.constructor(String, String).

Ambiguous means u must have two or more classes,methods or something with the same name.
Example

using UnityEngine;
using System.Collections;
using System;

public class Example : MonoBehaviour 
{
     public Object object_One;
    /* Now this  will throw an error saying  - Object is an ambiguous reference between    'UnityEngine.Object' and 'System.Object'  */
    

    //Inorder to avoid this you have to use namespace specific

    //For UnityEngine Object,use 
    public UnityEngine.Object UE_Object;

    //For System Object,use
    public System.Object Sys_Object
}