I've read a few posts on this board and others regarding problems with using POST in Netscape 6 forms. Finally I've experieced this myself.
Here's the bug report from Bugzilla:
http://bugzilla.mozilla.org/show_bug.cgi?id=41241
This is a very real problem and can occur at any time. No idea why, but it does happen. By simply sending my form variables to the next page with JavaScript, I got to work:
CODE:
<?php
echo("<script>");
echo("location.href='page.php?".session_name()."=".session_id()."'");
echo("</script>");
?>
Hope this helps someone. Remember, use GET or try and find another way via JavaScript or something. The code above uses a session but it could be any form variables.