Error message

• Warning: Cannot modify header information - headers already sent by (output started at /home/optimadecisi/public_html/includes/common.inc:2726) in drupal_send_headers() (line 1233 of /home/optimadecisi/public_html/includes/bootstrap.inc).
• Error: Call to undefined function lock_may_be_available() in lock_acquire() (line 146 of /home/optimadecisi/public_html/includes/lock.inc).