Marketpress Warning: session_start() [function.session-start]: Cannot send session cookie - headers

I updated my marketpress recently on a single-site install.
I am on godaddy hosting (likely a mistake..).

I continue to get this message on the checkout page of my test site:
Warning: session_start() [function.session-start]: Cannot send session cookie - headers already sent by (output started at /home/content/05/7620705/html/naw/index.php:1) in /home/content/05/7620705/html/naw/wp-content/plugins/marketpress/marketpress.php on line 848

Prod site has not been updated/touched, but all of sudden is experiencing a similar error. Would you please advise?

What I've tried:
1). adding a sessions folder and modifying wp-config - revertered after fail.
2). adding a sessions folder and modifying wp-config and marketpress.php - reverted after fail.
3). disabling all other plugins and trying 1&2 again. No luck.

Test site: http://naw.packanimalcreative.com
Prod site: http://bromerica.com