Index: wp-comments-post.php
===================================================================
--- wp-comments-post.php	(revision 39949)
+++ wp-comments-post.php	(working copy)
@@ -28,7 +28,7 @@
 	if ( ! empty( $data ) ) {
 		wp_die( '<p>' . $comment->get_error_message() . '</p>', __( 'Comment Submission Failure' ), array( 'response' => $data, 'back_link' => true ) );
 	} else {
-		exit;
+		wp_die( '<p>' . $comment->get_error_message() . '</p>', __( 'Comment Submission Failure' ), array( 'back_link' => true ) );
 	}
 }
 
Index: wp-includes/comment.php
===================================================================
--- wp-includes/comment.php	(revision 39949)
+++ wp-includes/comment.php	(working copy)
@@ -2956,7 +2956,7 @@
 		 */
 		do_action( 'comment_id_not_found', $comment_post_ID );
 
-		return new WP_Error( 'comment_id_not_found' );
+		return new WP_Error( 'comment_id_not_found', __( 'Sorry, comments are not allowed for this item.' ), 403 );
 
 	}
 
@@ -2964,7 +2964,7 @@
 	$status = get_post_status( $post );
 
 	if ( ( 'private' == $status ) && ! current_user_can( 'read_post', $comment_post_ID ) ) {
-		return new WP_Error( 'comment_id_not_found' );
+		return new WP_Error( 'comment_id_not_found', __( 'Sorry, comments are not allowed for this item.' ), 403 );
 	}
 
 	$status_obj = get_post_status_object( $status );
@@ -2993,7 +2993,7 @@
 		 */
 		do_action( 'comment_on_trash', $comment_post_ID );
 
-		return new WP_Error( 'comment_on_trash' );
+		return new WP_Error( 'comment_on_trash', __( 'Sorry, comments are not allowed for this item.' ), 403 );
 
 	} elseif ( ! $status_obj->public && ! $status_obj->private ) {
 
@@ -3006,7 +3006,7 @@
 		 */
 		do_action( 'comment_on_draft', $comment_post_ID );
 
-		return new WP_Error( 'comment_on_draft' );
+		return new WP_Error( 'comment_on_draft', __( 'Sorry, comments are not allowed for this item.' ), 403 );
 
 	} elseif ( post_password_required( $comment_post_ID ) ) {
 
@@ -3019,7 +3019,7 @@
 		 */
 		do_action( 'comment_on_password_protected', $comment_post_ID );
 
-		return new WP_Error( 'comment_on_password_protected' );
+		return new WP_Error( 'comment_on_password_protected', __( 'Sorry, comments are not allowed for this item.' ), 403 );
 
 	} else {