I did noting ,when try to clear cache I see this error Catchable fatal error: Object of class stdClass could not be converted to string includes/theme.inc on line 2742

foreach (array_keys($regions) as $region) {
    // Assign region to a region variable.
    $region_content = drupal_get_region_content($region);
//  $tmp = (array) $variables[$region];
    //ym(empty($tmp));
//  if(empty($tmp))
    isset($variables[$region]) ? $variables[$region] .= $region_content : $variables[$region] = $region_content;

I google this error but didn't find anything, anybody know what is the reason of this error and how can I resolve it?