Hi, I am getting this warning when I click on my product links.

Warning: Cannot modify header information - headers already sent by (output started at /home/content/b/a/c/backdoor45/html/catalog/includes/languages/english/index.php:1) in /home/content/b/a/c/backdoor45/html/catalog/includes/functions/functions_general.php on line 44

 Does anyone know what this means, and how to fix it?
Thank you, Karole