I keep getting "headers already sent" whilst trying to use sessions

"Warning: Cannot send session cookie - headers already sent by (output  started at c:\wwwroot\somesite\cart.php3:9) in c:\wwwroot\somesite\cart.php3 on line 11 

Check through your code prior to the session_start(); command.

You will have sent some text to the browser, and since headers (and cookies which are contained within headers) need to be sent before any output, this causes the error. Look for any print, printf, or echo commands. Also look for whitespaces, tabs etc. before the session_start();

Look for include('file') statements, they might be causing the problem.