Error message with Facebook connect

[C5rider]

I just activated Facebook connect on my forum (www.bench-racer.com) and now I am receiving this error message when you click the "Register" link. I didn't have this error message prior to the Facebook connect option. I am running PHP Version 5.6.22.

Warning: session_start(): Cannot send session cache limiter - headers already sent (output started at /home/benchrac/public_html/includes/vb5/frontend/controller/page.php:53) in .../vb/library/facebook.php on line 213

Thanks!