(Solved) Google Play Games setup problem: "Invalid classname"

I can’t set up google play games for android. After pressing the setup button, I just get “Invalid classname: Object reference not set to an instance of an object.” How can I fix this?

It seems to have solved itself after I installed voxelbusters native share. I don’t know what was wrong or missing.

I’ve actually just started getting this issue. I’m unsure why.

same