Error message

• Warning: Undefined variable $key in comment_prepare_thread() (line 901 of /home/educati3/edtechtalk.com/modules/comment/comment.module).
• Warning: Cannot modify header information - headers already sent by (output started at /home/educati3/edtechtalk.com/includes/common.inc:2822) in drupal_send_headers() (line 1551 of /home/educati3/edtechtalk.com/includes/bootstrap.inc).
• Error: Attempt to assign property "divs_final" on null in comment_prepare_thread() (line 901 of /home/educati3/edtechtalk.com/modules/comment/comment.module).