在PHP中设置cookie。 适用于FF和Chrome，但不适用于IE

I am trying to add a cookie, which works fine in firefox and chrome, but is not working in IE.

Here's the code:

ob_start( 'ob_gzhandler' );
header('P3P:CP="IDC DSP COR ADM DEVi TAIi PSA PSD IVAi IVDi CONi HIS OUR IND CNT"');

$expires = time()+60*60*24*30;
setcookie( 'aff_source', $value, $expires, '/', '.subdomain.domain.in', false, true );

I am not sure why it's not setting the cookie in IE. Would appreciate any pointers.

IE version: 8
Checked with  - IE developer toolbar

I have looked at the answers in SO for similar problems, but am not able to solve it.

Thanks.