Sessions in PHP

Hi friends,
Iam new to PHP. I am using sessions in authenticating user and in some other php files.

My code is as follows....

<?
session_start();
header("Cache-control: private"); //IE 6 Fix

some other php code to do other tasks....

some html code...etc....

BUT IM Getting the following error,

Warning: Cannot send session cache limiter - headers already sent (output started at .....file info....

Warning: Cannot add header information - headers already sent by......

Can someone tell me what is the problem with sessions here.
I have experience in JSP's ColdFusion and ASP.

Thanks for your help and time.
KK.

you can't have any output at all before your header, so check for blank spaces or lines at the beginning of your file, or in included files, if any.

check to see, and make sure that this is first item on the page after <?php no spaces before any of these

<?
session_start();
header("Cache-control: private"); //IE 6 Fix

some other php code to do other tasks....

has to be first thing on the page
hth

Yep, I could figure it out.
Thanks for your time.