open the file mentioned:
Index: wp-includes/comment.php
===================================================================
--- wp-includes/comment.php (revision 2072)
+++ wp-includes/comment.php (working copy)
@@ -983,7 +983,7 @@
$commentdata['comment_parent'] = ( 'approved' == $parent_status || 'unapproved' == $parent_status ) ? $commentdata['comment_parent'] : 0;
$commentdata['comment_author_IP'] = preg_replace( '/[^0-9a-fA-F:., ]/', '',$_SERVER['REMOTE_ADDR'] );
- $commentdata['comment_agent'] = $_SERVER['HTTP_USER_AGENT'];
+ $commentdata['comment_agent'] = substr($_SERVER['HTTP_USER_AGENT'], 0, 255);
$commentdata['comment_date'] = current_time('mysql');
$commentdata['comment_date_gmt'] = current_time('mysql', 1);
find this line:
$commentdata['comment_agent'] = $_SERVER['HTTP_USER_AGENT'];
remove it and replace it with this line:
$commentdata['comment_agent'] = substr($_SERVER['HTTP_USER_AGENT'], 0, 255);