sessions not persisting inside an iframe

I have a site where a user can type a URL into a textbox and click submit, and that URL loads in an iframe.

My problem is that if the site that loads in the iframe uses sessions, and the user wants to log in, they are constantly logged out again (it seems the sessions aren't 'sticking').

Is this something I can fix, or is it normal browser behavior? Is there any workaround so users can stay logged in to the site they have chosen to load inside my iframe?

The site mentioned above works perfectly in Netscape 7.2. Apparently this is just an IE problem. Is there a solution? 100% of my users use IE (internal site with controlled environments), so it working in Netscape is of no use to me.

you could try passing the session ID..
I googled to see if anyone else had been experiencing a similar problem:
http://www.sitepoint.com/forums/showthread.php?t=154678

I couldn't pass the session variable, because the site inside the iframe could be any site on the net (the src is entered by the user into a form). I have no control over what happens inside that iframe. Thanks for the suggestion though.

I did however discover that the problem lies in the security settings for IE6. There is another thread on that here already.
http://www.codingforums.com/showthread.php?t=14424

Since I don't have access to the sites inside the iframe to add the line of code as specified in this other thread, instead I changed my security settings to allow third party cookies. Now we just have to change the settings for each of our users. And that is someone else's job.