Error message

• Notice: Undefined index: search_block_form in drupal_retrieve_form() (line 809 of /home/powder/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 844 of /home/powder/public_html/includes/form.inc).