Parsing Error

I went to wp-includes/kes.php to comment out a few html tags. After that, I went to my comment moderation area in the admin to approve a few comments, and I got this error:
Warning: Cannot modify header information – headers already sent by (output started at /home/lashawnb/public_html/wp-includes/kses.php:570) in /home/lashawnb/public_html/wp-admin/moderation.php on line 87
I didn’t go into wp-admin/moderation. Can anyone tell me what I need to do? Thanks.