"An internal error occurred" with integration of Google Plus Login
I have this problem and even after creating 10 different client IDs with different SHA and package name, it doesn't work... until I found out that you have to fill the Consent screen.
According to GoogleDevelopers Console -
The consent screen will be shown to users whenever you request access to their private data using your client ID.
This can happen when you haven't set the signature for the client ID in your API console project, or if you copied the wrong key value from keytool. Doing so is documented in the steps of the quick start guide on steps 7, 8, 9, and 10.
I've solved problem by removing .setScopes("PLUS_LOGIN") in the PlusClient.Builder.