Problem with Google Play Game Services: Invalid Classname

This is the first time that I put in one game the Google Play Game Services.

I’ve read all the tutorial of GitHub and I’ve followed the steps, I have everything downloaded (the google play games services, the google repository, etc.) but when I click to the setup button in the game resources (going to Window → Google Play Games → Setup → Android Setup) it launches me an error: Invalid classname: Exception has been thrown by the target of an invocation.

Despite this, the resources file is generated.

What does it mean? Should not I worry?

this issue is duplicated plugin file

  1. remove all plugin
  2. use play-games-plugin-for-unity-0.9.41
    my game work fine perfect
    https://play.google.com/store/apps/details?id=com.zskull.blocks