Getting Cannot send session cache limiter - headers already sent (output started at

[catalepticstate]

<b>Warning</b>: session_start() [<a href='function.session-start'>function.session-start</a>]: Cannot send session cache limiter - headers already sent (output started at /home/site/public_html/cards/card_index.php:2) in <b>/home/site/public_html/cards/includes/functions/sessions.php</b> on line <b>102</b><br />

 

Why am I getting this?