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 (
  'date' => 'Wed, Apr 24',
  'previousPages' => 
  Piwik\DataTable::__set_state(array(
     'rows' => 
    array (
      0 => 
      Piwik\DataTable\Row::__set_state(array(
         'maxVisitsSummed' => 0,
         'columns' => 
        array (
          'label' => 'friedrichshagen.net/vereine/werbegemeinschaft-friedrichshagen-ev/theaterkasse/',
          'referrals' => 2,
        ),
         'metadata' => 
        array (
        ),
         'isSubtableLoaded' => false,
         'subtableId' => NULL,
      )),
    ),
     'currentId' => 1,
     'depthLevel' => 0,
     'indexNotUpToDate' => true,
     'rebuildIndexContinuously' => false,
     'tableSortedBy' => false,
     'queuedFilters' => 
    array (
    ),
     'disabledFilters' => 
    array (
    ),
     'rowsCountBeforeLimitFilter' => 0,
     'enableRecursiveSort' => false,
     'enableRecursiveFilters' => false,
     'rowsIndexByLabel' => 
    array (
    ),
     'summaryRow' => NULL,
     'metadata' => 
    array (
    ),
     'maximumAllowedRows' => 0,
  )),
  'previousSiteSearches' => 
  Piwik\DataTable::__set_state(array(
     'rows' => 
    array (
    ),
     'currentId' => 2,
     'depthLevel' => 0,
     'indexNotUpToDate' => true,
     'rebuildIndexContinuously' => false,
     'tableSortedBy' => false,
     'queuedFilters' => 
    array (
    ),
     'disabledFilters' => 
    array (
    ),
     'rowsCountBeforeLimitFilter' => 0,
     'enableRecursiveSort' => false,
     'enableRecursiveFilters' => false,
     'rowsIndexByLabel' => 
    array (
    ),
     'summaryRow' => NULL,
     'metadata' => 
    array (
    ),
     'maximumAllowedRows' => 0,
  )),
  'pageMetrics' => 
  array (
    'loops' => 1,
    'pageviews' => 3,
    'entries' => 0,
    'exits' => -71,
  ),
  'followingPages' => 
  Piwik\DataTable::__set_state(array(
     'rows' => 
    array (
      0 => 
      Piwik\DataTable\Row::__set_state(array(
         'maxVisitsSummed' => 0,
         'columns' => 
        array (
          'label' => 'friedrichshagen.net/vereine/werbegemeinschaft-friedrichshagen-ev/fest-auf-der-boelsche/',
          'referrals' => 4,
        ),
         'metadata' => 
        array (
        ),
         'isSubtableLoaded' => false,
         'subtableId' => NULL,
      )),
      1 => 
      Piwik\DataTable\Row::__set_state(array(
         'maxVisitsSummed' => 0,
         'columns' => 
        array (
          'label' => 'friedrichshagen.net/start/willkommen-in-friedrichshagen/',
          'referrals' => 4,
        ),
         'metadata' => 
        array (
        ),
         'isSubtableLoaded' => false,
         'subtableId' => NULL,
      )),
      2 => 
      Piwik\DataTable\Row::__set_state(array(
         'maxVisitsSummed' => 0,
         'columns' => 
        array (
          'label' => 'friedrichshagen.net/gesundheit/pflegestuetzpunkt-treptow-koepenick/',
          'referrals' => 3,
        ),
         'metadata' => 
        array (
        ),
         'isSubtableLoaded' => false,
         'subtableId' => NULL,
      )),
      3 => 
      Piwik\DataTable\Row::__set_state(array(
         'maxVisitsSummed' => 0,
         'columns' => 
        array (
          'label' => 'friedrichshagen.net/start/willkommen-in-friedrichshagen/nachrichtendetails/?no_cache=1&tx_ttnews[tt_news]=5865',
          'referrals' => 2,
        ),
         'metadata' => 
        array (
        ),
         'isSubtableLoaded' => false,
         'subtableId' => NULL,
      )),
      4 => 
      Piwik\DataTable\Row::__set_state(array(
         'maxVisitsSummed' => 0,
         'columns' => 
        array (
          'label' => 'friedrichshagen.net/historisches/chronik/',
          'referrals' => 2,
        ),
         'metadata' => 
        array (
        ),
         'isSubtableLoaded' => false,
         'subtableId' => NULL,
      )),
      5 => 
      Piwik\DataTable\Row::__set_state(array(
         'maxVisitsSummed' => 0,
         'columns' => 
        array (
          'label' => 'Others',
          'referrals' => 58,
        ),
         'metadata' => 
        array (
        ),
         'isSubtableLoaded' => false,
         'subtableId' => NULL,
      )),
    ),
     'currentId' => 3,
     'depthLevel' => 0,
     'indexNotUpToDate' => true,
     'rebuildIndexContinuously' => false,
     'tableSortedBy' => false,
     'queuedFilters' => 
    array (
    ),
     'disabledFilters' => 
    array (
    ),
     'rowsCountBeforeLimitFilter' => 0,
     'enableRecursiveSort' => false,
     'enableRecursiveFilters' => false,
     'rowsIndexByLabel' => 
    array (
    ),
     'summaryRow' => NULL,
     'metadata' => 
    array (
    ),
     'maximumAllowedRows' => 0,
  )),
  'followingSiteSearches' => 
  Piwik\DataTable::__set_state(array(
     'rows' => 
    array (
    ),
     'currentId' => 4,
     'depthLevel' => 0,
     'indexNotUpToDate' => true,
     'rebuildIndexContinuously' => false,
     'tableSortedBy' => false,
     'queuedFilters' => 
    array (
    ),
     'disabledFilters' => 
    array (
    ),
     'rowsCountBeforeLimitFilter' => 0,
     'enableRecursiveSort' => false,
     'enableRecursiveFilters' => false,
     'rowsIndexByLabel' => 
    array (
    ),
     'summaryRow' => NULL,
     'metadata' => 
    array (
    ),
     'maximumAllowedRows' => 0,
  )),
  'outlinks' => 
  Piwik\DataTable::__set_state(array(
     'rows' => 
    array (
    ),
     'currentId' => 5,
     'depthLevel' => 0,
     'indexNotUpToDate' => true,
     'rebuildIndexContinuously' => false,
     'tableSortedBy' => false,
     'queuedFilters' => 
    array (
    ),
     'disabledFilters' => 
    array (
    ),
     'rowsCountBeforeLimitFilter' => 0,
     'enableRecursiveSort' => false,
     'enableRecursiveFilters' => false,
     'rowsIndexByLabel' => 
    array (
    ),
     'summaryRow' => NULL,
     'metadata' => 
    array (
    ),
     'maximumAllowedRows' => 0,
  )),
  'downloads' => 
  Piwik\DataTable::__set_state(array(
     'rows' => 
    array (
    ),
     'currentId' => 6,
     'depthLevel' => 0,
     'indexNotUpToDate' => true,
     'rebuildIndexContinuously' => false,
     'tableSortedBy' => false,
     'queuedFilters' => 
    array (
    ),
     'disabledFilters' => 
    array (
    ),
     'rowsCountBeforeLimitFilter' => 0,
     'enableRecursiveSort' => false,
     'enableRecursiveFilters' => false,
     'rowsIndexByLabel' => 
    array (
    ),
     'summaryRow' => NULL,
     'metadata' => 
    array (
    ),
     'maximumAllowedRows' => 0,
  )),
  'referrers' => 
  array (
    0 => 
    array (
      'label' => 'Direct Entries',
      'shortName' => 'Direct Entry',
      'visits' => 0,
    ),
  ),
);