Error pages after adding a second sidebar/modifying functions.php

Hi, I keep getting error messages along similar lines to the following:

Warning: Cannot modify header information – headers already sent by (output started at /home5/backlane/public_html/wp-content/themes/starkers/functions.php:3) in /home5/backlane/public_html/wp-includes/pluggable.php on line 865

It happens during plugin installations through dashboard, and also when I take the www. off my urls.

I first noticed the problem occuring after following the instructions on this website (http://www.blogohblog.com/adding-extra-sidebar-to-your-wordpress-theme/) to create a new sidebar, and I think when I edited the functions php file, something was upset. I have been trying to find other threads on similar problems, but it’s difficult to describe to a search engine the problem. Anyone have any ideas?