How would I go about fixing this...

[19-Mar-2009 09:04:33] PHP Warning: session_start() [<a href='function.session-start'>function.session-start</a>]: Cannot send session cache limiter - headers already sent (output started at /home3/maximum6/public_html/store/index.php:2) in /home3/maximum6/public_html/store/includes/functions/sessions.php on line 108
[19-Mar-2009 09:04:33] PHP Warning: Cannot modify header information - headers already sent by (output started at /home3/maximum6/public_html/store/index.php:2) in /home3/maximum6/public_html/store/includes/init_includes/init_templates.php on line 78
[19-Mar-2009 09:04:33] PHP Warning: require(includes/main_cart_actions.php) [<a href='function.require'>function.require</a>]: failed to open stream: No such file or directory in /home3/maximum6/public_html/store/includes/init_includes/init_cart_handler.php on line 36
[19-Mar-2009 09:04:33] PHP Fatal error: require() [<a href='function.require'>function.require</a>]: Failed opening required 'includes/main_cart_actions.php' (include_path='.:/usr/lib/php:/usr/local/lib/php') in /home3/maximum6/public_html/store/includes/init_includes/init_cart_handler.php on line 36