Error message

• Warning: Cannot modify header information - headers already sent by (output started at /var/www/html/elmsln_community/api.elmsln.org/includes/common.inc:2791) in drupal_send_headers() (line 1499 of /var/www/html/elmsln_community/api.elmsln.org/includes/bootstrap.inc).
• Error: Call to undefined function apc_delete() in DrupalAPCCache->clear() (line 289 of /var/www/html/elmsln_community/api.elmsln.org/sites/all/modules/apc/drupal_apc_cache.inc).