Comments unapprove bug!

I dont know if anybody else is having this problem, maybe only me, but when i try to Unapprove an comment at this page:/wp-admin/edit.php

i’m geting this:

Warning: Cannot modify header information – headers already sent by (output started at /home/misiune/public_html/misiune/wp-admin/admin-header.php:8) in /home/misiune/public_html/misiune/wp-admin/post.php on line 586

i have the last version of WP.

tnq.