I was having the same problem, and for anyone still wondering, here's how you fix it:
In the "
wp-includes" folder, locate the file "
comment.php" and open this with a text editor. (ie: Notepad or TextEdit) Do a quick find (Edit > Find) for the word
duplicate and you'll arrive at these lines of code.
// Simple duplicate check
expected_slashed ($comment_post_ID, $comment_author, $comment_author_email, $comment_content)
$dupe = "SELECT comment_ID FROM $wpdb->comments WHERE comment_post_ID = '$comment_post_ID' AND ( comment_author = '$comment_author' ";
if ( $comment_author_email )
$dupe .= "OR comment_author_email = '$comment_author_email' ";
$dupe .= ") AND comment_content = '$comment_content' LIMIT 1";
if ( $wpdb->get_var($dupe) )
wp_die( __('Duplicate comment detected; it looks as though you\'ve already said that!') );
You can delete this code completely or mark it as comments with two forward slashes at the beginning of each line
Delete it if you never want to see it again, and comment it if you wish to keep it for a later use.
Once complete, save it and upload it to the appropriate location on your web server.
Ta da! Go post the same comment twice, no one cares any more.
Please note that future upgrades to WordPress may very well overwrite your comments.php that you just edited, and you may need to do this again.