PHP Sessions and SSL

Hi, I am currently developing a site which makes use of SSL and sessions. However, sometimes when I submit form data (from an SSL page to another SSL page on the same server), I get an error saying "This page contains both secure and unsecure items. Do you want to display the nonsecure items" (I have had these results in IE5.5 and IE6, possibly IE5 too). If I press yes, a DNS error page appears. If i press no, a page saying simply "NavigationCancelled" (without any spaces) appears. This error seems to happen randomly, and only when form data is being sent with POST (I haven't tried it with GET or anything else as it may be a security risk to have the form contents displayed in the query string). I have found a way to fix this, however, it had some undesirable affects with pages being cashed (and therefore not being displayed with any changed session variables). This "fix" was done using session_cache_limiter('private'), but I don't want to use this due to these caching effects. Does anyone have any suggestions that could fix this problem? I would be very grateful. Richard Hilton