Header error

Hi,

First, here’s a link to the site I’m developing: https://www.velocitybranding.com/pauline

My client gets the following error when she tries to view the site (I don’t get the error when I view it):

Warning: Cannot modify header information – headers already sent by (output started at /home/velocity/public_html/pauline/wp-content/themes/thematic_pauline/functions.php:56) in /home/velocity/public_html/pauline/wp-includes/pluggable.php on line 897

I am a bit of a php rookie so I have no idea what that means. I’ve stripped out anything to do with the header from my functions.php file and here’s what line 897 says in pluggable.php:

header("Location: $location", true, $status);
}
endif;

Any ideas of what I can do? Please be specific, I am seriously a rookie at this stuff.

Thanks in advance!