Session lost using iframe in IE

[VP.]

I found this solution here and a few other places on google:  http://www.phpfreaks.com/forums/index.php/topic,157539.0.html

 

Unfortunately I can't seem to get this working in mine.  Maybe I'm including that header line in the wrong file?  Here's the situation:

 

I have a main.php file that contains an iframe and a couple of other php includes.  The php includes need to be able to share the same session array as the one in the iframe.  Which of these files should I include

 

header('P3P: CP="CAO PSA OUR"');