Warning: session_start() [function.session-start] headers already sent [duplicate]

This question already has an answer here:

• How to fix “Headers already sent” error in PHP 12 answers

I have my Opencart webshop updated to the latest version.. Now I get the following error on the admin page.

Warning: session_start() [function.session-start]: Cannot send session cache limiter - headers already sent (output started at /home/barbecue/domains/http://ift.tt/1P3G0oh) in /home/barbecue/domains/http://ift.tt/1hhxh6P on line 17

What should I do?

via Chebli Mohamed