play-games-plugin-for-unity Authentication issue

I have downloaded the google play service form GitHub - playgameservices/play-games-plugin-for-unity: Google Play Games plugin for Unity. i have followed the tutorial on github and implemented it. When i click on log in button nothing happened. Here is the code.

using UnityEngine;
using System.Collections;
using GooglePlayGames;
using UnityEngine.SocialPlatforms;

public class testGPGMenu : MonoBehaviour
{

public GUISkin skin;
public int incrementalCount = 5;

//leaderboard strings
private string leaderboard = "C----------------g";
//achievement strings
private string achievement = "C----------------Q";
private string incremental = "C----------------g";

// Use this for initialization
void Start()
{
    PlayGamesPlatform.Activate();
}

// Update is called once per frame
public void OnGUI()
{
    GUI.skin = skin;
    skin.button.fixedWidth = Screen.width - 25;
    skin.textField.fixedWidth = Screen.width - 25;
    GUILayout.BeginArea(new Rect(0, 0, Screen.width, Screen.height));

    GUILayout.BeginVertical("box");

    GUILayout.Label("Official Google Play Games Services");

    GUILayout.Space(20);

    //Share Status
    if (GUILayout.Button("Log In"))
    {
        Social.localUser.Authenticate((bool success) =>
                                      {
            if (success)
            {
                Debug.Log("You've successfully logged in");
            }
            else
            {
                Debug.Log("Login failed for some reason");
            }
        });
    }

    GUILayout.Space(20);

    //Achievement
    if (GUILayout.Button("Unlock Achievement"))
    {
        if (Social.localUser.authenticated)
        {
            Social.ReportProgress(achievement, 100.0f, (bool success) =>
                                  {
                if (success)
                {
                    Debug.Log("You've successfully logged in");
                }
                else
                {
                    Debug.Log("Login failed for some reason");
                }
            });
        }
    }

    GUILayout.Space(20);

    //Incremental Achievement
    if (GUILayout.Button("Press " + incrementalCount + "more times to unlock incremental acheivment"))
    {
        if (Social.localUser.authenticated)
        {
            ((PlayGamesPlatform)Social.Active).IncrementAchievement(incremental, 5, (bool success) =>
                                                                    {
                //The achievement unlocked successfully
            });
        }
    }

    GUILayout.Space(20);

    //Leaderboard
    if (GUILayout.Button("Post your 5000 points to the leaderboard"))
    {
        if (Social.localUser.authenticated)
        {
            Social.ReportScore(5000, leaderboard, (bool success) =>
                               {
                if (success)
                {
                    ((PlayGamesPlatform)Social.Active).ShowLeaderboardUI(leaderboard);
                }
                else
                {
                    //Debug.Log("Login failed for some reason");
                }
            });
        }
    }

    GUILayout.Space(20);

    // Show Leaderboard
    if (GUILayout.Button("Show Leaderboard"))
    {
        Social.ShowLeaderboardUI();
    }

    GUILayout.Space(20);

    //Show Specific Leaderboard
    if (GUILayout.Button("Show Specific Leaderboard"))
    {
        ((PlayGamesPlatform)Social.Active).ShowLeaderboardUI(leaderboard);
    }

    GUILayout.Space(20);

    //Show Achievments
    if (GUILayout.Button("Show Achievments"))
    {
        Social.ShowAchievementsUI();
    }

    GUILayout.Space(20);

    //Sign Out
    if (GUILayout.Button("Sign Out"))
    {
        ((PlayGamesPlatform)Social.Active).SignOut();
    }

    GUILayout.EndVertical();
    GUILayout.EndArea();
}

}

Here is what i get in logcat
07-22 15:43:00.678: I/Unity(1222): NullReferenceException: Object reference not set to an instance of an object
07-22 15:43:00.678: I/Unity(1222): at GooglePlayGames.Android.AndroidClient+c__AnonStorey0.<>m__1 () [0x00000] in :0
07-22 15:43:00.678: I/Unity(1222): at UnityEngine.AndroidJavaRunnableProxy.run () [0x00000] in :0
07-22 15:43:00.678: I/Unity(1222): at System.Reflection.MonoMethod.Invoke (System.Object obj, BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object parameters, System.Globalization.CultureInfo culture) [0x00000] in :0
07-22 15:43:00.678: I/Unity(1222): Rethrow as TargetInvocationException: UnityEngine.AndroidJavaRunnableProxy.run()
07-22 15:43:00.678: I/Unity(1222): at UnityEngine.AndroidJavaProxy.Invoke (System.String methodName, System.Object args) [0x00000] in :0
07-22 15:43:00.678: I/Unity(1222): at UnityEngine.AndroidJavaProxy.Invoke (System.String methodName, UnityEngine.AndroidJavaObject javaArgs) [0x00000] in :0
07-22 15:43:00.678: I/Unity(1222): at UnityEngine._AndroidJNIHelper.InvokeJavaProxyMethod (UnityEngine.AndroidJavaProxy proxy, IntPtr jmethodName, IntPtr jargs) [0x00000] in :0

This Happened to me yesterday… u need to go to developer console then go to testing and activate Beta & Alpha testers… that simple

Hello Guys,

After 2 days of tests with Authentification problems, (ERROR_NOT_AUTHORIZED)
I spotted my mistake :
"PlayGamesClientConfiguration config = new PlayGamesClientConfiguration.Builder()
.EnableSavedGames()
.Build();
"
I wrotted : “.EnableSavedGames()” but my game don’t use it in Google Play interface, so the error occured !
Simply removing it (for my part), and let’s rock n roll !

i had the same issue…enable alpha testing from the developer console and add your mobile device email id to the console for testing