谷歌auth api只是返回'意外错误'

Question

        $client = new \Google_Client();
        $client->setApplicationName('AnalyticsAPI');
        $cred = new \Google_Auth_AssertionCredentials(
            '[e-mail]',
            array('https://www.googleapis.com/auth/analytics.readonly'),
            \file_get_contents( __DIR__ . '/../google-keys/AnalyticsAPI-XXX.p12' )
        );
        echo 'test1/';
        $client->setAssertionCredentials($cred);
        echo 'test2';
        if($client->getAuth()->isAccessTokenExpired()) {
            echo 'test3/';
            $client->getAuth()->refreshTokenWithAssertion($cred);
            echo 'test4/';
        }

The above php code spits out the following:

test1/test2/test3/An unexpected error has occurred. Please contact the webmaster.

This means that the error is happening when the code runs:

$client->getAuth()->refreshTokenWithAssertion($cred); 

I have checked and triple checked the serviceaccount.com email as well as the p12 key.. but i get nothing other than, unexpected error.

Has anyone else hit this wall before? I cannot see what is wrong with the code.

Following the post: refreshTokenWithAssertion Permission Denied

I altered the above code where it was failing to run a try catch, but the try does not fail!:

if($client->getAuth()->isAccessTokenExpired()) {
    try {
        $client->getAuth()->refreshTokenWithAssertion($cred);
    } catch (Exception $e) {
        echo 'Failed:';
        print_r($e->getMessage());
    }
}