@spellbound there is not a "Switch off meta-comments" configuration parameter, actually. However, you still have some options.

This feature is controlled by the "Permission to post meta comments into this collection" option at the Collection Permission screen (http://b2evolution.net/man/list-of-permissions), under the "Comment statuses" column. These permissions may be set per users or per groups, so unchecking that option for those groups/users where it's currently checked will disable meta-comments for them. However, Administrators and collection owners will keep their access to meta-comments intact due to the checkbox can't be unchecked, so you need to do the following:

1. Get rid of the meta-comments form in the front-office by overriding skins_fallback_v6/_item_meta_comments.inc.php, duplicating it into your skin folder and removing all the content (or just creating an empty file with the same name).
2. The back-office posts edition form is a way different matter. There is no standard way to remove the meta-comments section, so maybe you just want to hide the fieldset using CSS (dirty, cosmetic and not ideal, of course). In order to do it, just add #fieldset_wrapper_itemform_meta_cmnt{display:none;} at the very end of the skins_adm/bootstrap/rsc/css/style.min.css file (incorrect but quick way to edit CSS files in b2evolution). For the correct way, please see this page: http://b2evolution.net/man/grunt, and if you need more details, just ask for them.

Sorry for a long delay.Thank you,your method worked fine, There is no more metacomments on my blog, and it's great!