Error:  Data structure returned is not convertible in the requested format. Try to call this method with the parameters '&amp;format=original&amp;serialize=1'; you will get the original php data structure serialized. The data structure looks like this: 
 $data = array (
  0 =&gt; 
  array (
    'login' =&gt; 'admin',
    'email' =&gt; 'M.Jank@genesis-display.com',
    'superuser_access' =&gt; true,
    'date_registered' =&gt; '2014-03-06 11:24:44',
    'invited_by' =&gt; NULL,
    'invite_expired_at' =&gt; NULL,
    'invite_accept_at' =&gt; NULL,
    'role' =&gt; 'superuser',
    'capabilities' =&gt; 
    array (
    ),
    'last_seen' =&gt; '1327 days 11:39:22',
    'invite_status' =&gt; 'active',
    'uses_2fa' =&gt; false,
  ),
  1 =&gt; 
  array (
    'login' =&gt; 'anonymous',
    'email' =&gt; '',
    'superuser_access' =&gt; true,
    'date_registered' =&gt; '2013-11-01 09:33:05',
    'invited_by' =&gt; NULL,
    'invite_expired_at' =&gt; NULL,
    'invite_accept_at' =&gt; NULL,
    'role' =&gt; 'superuser',
    'capabilities' =&gt; 
    array (
    ),
    'last_seen' =&gt; '00:11:51',
    'invite_status' =&gt; 'active',
    'uses_2fa' =&gt; false,
  ),
);