While working on a Drupal site, we kept getting error messages after deleting content:

•	recoverable fatal error: Object of class stdClass could not be 
converted to string in /usr/local/drupal/includes/bootstrap.inc on line 768.
•	warning: preg_match() expects parameter 2 to be string, object given 
in /usr/local/drupal/includes/bootstrap.inc on line 771.

after that we got a similar error but on line 735

we looked around for a bit and fixed it. we edited the bootstrap file, which is actually not done. if anyone found a better way to fix this issue, please comment on this post.

Anyway, this is what the bootstrap looks like now:

we changed lines 734 – 739:

function check_plain($text) {
 if(!is_string($text)){
 return "";
 }
 return drupal_validate_utf8($text) ? htmlspecialchars($text, ENT_QUOTES) : '';
}

and lines 770 – 775:

function drupal_validate_utf8($text) {
  if (!is_string($text) || strlen($text) == 0) {
    return TRUE;
  }
  return (preg_match('/^./us', $text) == 1);
}