Can’t modify header information

I have wordpress 2.7 and this is a message which I get when I try to run the blog’s page:

Warning: Cannot modify header information – headers already sent by (output started at /home/xphile/domains/xphile.info/public_html/pl/wp-content/themes/intraWP/functions.php:153) in /home/xphile/domains/xphile.info/public_html/pl/wp-includes/pluggable.php on line 850

I can’t go to the admin’s panel and don’t know what to do. Any ideas?