Error message

• Notice: Undefined index: search_block_form in drupal_retrieve_form() (line 806 of /home/quebecentreprise/public_html/includes/form.inc).
• Warning: call_user_func_array() expects parameter 1 to be a valid callback, function 'search_block_form' not found or invalid function name in drupal_retrieve_form() (line 841 of /home/quebecentreprise/public_html/includes/form.inc).