Error message

• Warning: Cannot modify header information - headers already sent by (output started at /home/kakapokids/public_html/includes/bootstrap.inc:1640) in drupal_send_headers() (line 1499 of /home/kakapokids/public_html/includes/bootstrap.inc).
• Error: Class 'SimpleXMLElement' not found in update_parse_xml() (line 390 of /home/kakapokids/public_html/modules/update/update.fetch.inc).