Marketpress.php on line 763

Here is the message I am getting when I go to the cart on my site: hho.bleupelikan.com

Any help in what is going on would be appreciated. Is this a MarketPress issue or a Standard Theme 2.0 issue?

Warning: session_start() [function.session-start]: Cannot send session cookie - headers already sent by (output started at /home/bleupel/public_html/hho/wp-content/themes/StandardTheme_254/lib/standard_theme_nav_walker.php:103) in /home/bleupel/public_html/hho/wp-content/plugins/marketpress/marketpress.php on line 763

Warning: session_start() [function.session-start]: Cannot send session cache limiter - headers already sent (output started at /home/bleupel/public_html/hho/wp-content/themes/StandardTheme_254/lib/standard_theme_nav_walker.php:103) in /home/bleupel/public_html/hho/wp-content/plugins/marketpress/marketpress.php on line 763

Thanks,
Greg