This happens when you try to start session more than once.
[php]
The solution for above problem is
1) in php.ini file set session.autostart to 0
session.auto_start = 0
2) Placing a .htaccess file in the root of your web directory with the following value:
php_flag session.auto_start 0
3) In your code use this line
if (!session_id()) session_start();
instead of
session_start();
[/php]