Error message

• Warning: Cannot modify header information - headers already sent by (output started at /home/lj88522/public_html/d7/includes/common.inc:2791) in drupal_send_headers() (line 1232 of /home/lj88522/public_html/d7/includes/bootstrap.inc).
• Error: Call to undefined function drupal_file_scan_write_cache() in drupal_page_footer() (line 2797 of /home/lj88522/public_html/d7/includes/common.inc).