Error loading admin page

When I go to my admin page, http://www.erinklema.com/wp-admin/, I receive this error message:

Warning: Cannot modify header information – headers already sent by (output started at /home/content/93/8365193/html/wp-content/themes/twentyeleven/functions.php:1) in /home/content/93/8365193/html/wp-includes/pluggable.php on line 934

Does anyone have any idea what that means and how I can fix it in order to log in to update my website?

Website: http://www.erinklema.com

Thank you for any help you can offer!