When running the install script, after only changing the config.php I encounter the following:

Warning: Cannot modify header information - headers already sent by (output started at /home/ucstudents.nl/public_html/bbpress/config.php:1) in /home/ucstudents.nl/public_html/bbpress/bb-admin/install.php on line 10
Warning: Cannot modify header information - headers already sent by (output started at /home/ucstudents.nl/public_html/bbpress/config.php:1) in /home/ucstudents.nl/public_html/bbpress/bb-includes/functions.php on line 1910
I can complete the installation but every page I visit starts with 
and other errors sometimes occur.
What is causing this, and how can it be fixed?