Error:  Data structure returned is not convertible in the requested format. Try to call this method with the parameters '&format=original&serialize=1'; you will get the original php data structure serialized. The data structure looks like this: 
 $data = array (
  0 => 
  array (
    'scope' => 'visit',
    'index' => 1,
    'usages' => 
    array (
    ),
  ),
  1 => 
  array (
    'scope' => 'visit',
    'index' => 2,
    'usages' => 
    array (
    ),
  ),
  2 => 
  array (
    'scope' => 'visit',
    'index' => 3,
    'usages' => 
    array (
    ),
  ),
  3 => 
  array (
    'scope' => 'visit',
    'index' => 4,
    'usages' => 
    array (
    ),
  ),
  4 => 
  array (
    'scope' => 'visit',
    'index' => 5,
    'usages' => 
    array (
    ),
  ),
  5 => 
  array (
    'scope' => 'page',
    'index' => 1,
    'usages' => 
    array (
    ),
  ),
  6 => 
  array (
    'scope' => 'page',
    'index' => 2,
    'usages' => 
    array (
    ),
  ),
  7 => 
  array (
    'scope' => 'page',
    'index' => 3,
    'usages' => 
    array (
    ),
  ),
  8 => 
  array (
    'scope' => 'page',
    'index' => 4,
    'usages' => 
    array (
    ),
  ),
  9 => 
  array (
    'scope' => 'page',
    'index' => 5,
    'usages' => 
    array (
    ),
  ),
);