I get error that prevent loading page to modify an extention group.

$padding_store[$row['parent_id']]; was undefined on line 798, so error was displayed at the beggining of the output, and cause error on further header send in index.php.

The reason was because $auth->acl_get('f_list', $row['forum_id']) was wrong on the parent, so the parent was not in $padding_store.

Reproductible : always , define a forum with acl f_list forbiden and a subforum with f_list enable, then try to modify an attachement group => impossible.

Solution : maybe on line 790 :

if (!isset($padding_store[$row['parent_id']]))
{
continue;
}