GoogleApiClient.isConnected() expects type interface but finds type virtual

Any ideas what to check in the library and extras setup on B4a 6.00? I started getting this error when the app starts (it compiles fine). App compiled fine (on a new PC via project zip) then I added the FirebaseMessaging service (just dropped in the example) then it starts throwing this error:

Code:

  java.lang.IncompatibleClassChangeError: The method 'boolean com.google.android.gms.common.api.GoogleApiClient.isConnected()' was expected to be of type interface but instead was found to be of...  

GoogleApiClient.isConnected() expects type interface but finds type virtual

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