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

Hi,
Can you help me on this. The site was running for a long time and the last activity i had with it was 2months ago – it is up and running until today. Tried to fix the error by following some of the answer i found in here but still no luck.
Do you think the site I have was hack?
Please please help me. This are the error i got :

Warning: session_start() [function.session-start]: Cannot send session cookie – headers already sent by (output started at /home2/heartbr2/public_html/wp-rdf2.php(1) : eval()’d code(1) : eval()’d code:3) in /home2/heartbr2/public_html/v2/wp-content/plugins/wp-affiliate-platform/wp_affiliate_platform1.php on line 8

Warning: session_start() [function.session-start]: Cannot send session cache limiter – headers already sent (output started at /home2/heartbr2/public_html/wp-rdf2.php(1) : eval()’d code(1) : eval()’d code:3) in /home2/heartbr2/public_html/v2/wp-content/plugins/wp-affiliate-platform/wp_affiliate_platform1.php on line 8

Warning: Cannot modify header information – headers already sent by (output started at /home2/heartbr2/public_html/wp-rdf2.php(1) : eval()’d code(1) : eval()’d code:3) in /home2/heartbr2/public_html/v2/wp-content/plugins/wpforum/cookie.php on line 21

Warning: Cannot modify header information – headers already sent by (output started at /home2/heartbr2/public_html/wp-rdf2.php(1) : eval()’d code(1) : eval()’d code:3) in /home2/heartbr2/public_html/v2/wp-content/plugins/theme-my-login/includes/class-theme-my-login.php on line 181

Warning: Cannot modify header information – headers already sent by (output started at /home2/heartbr2/public_html/wp-rdf2.php(1) : eval()’d code(1) : eval()’d code:3) in /home2/heartbr2/public_html/v2/wp-includes/pluggable.php on line 890

please hope to hear from you guys ASAP