_POST and Session ending Problem

Hello, I created a membership script. It was working fine. Members can fill out form and send it and they can continue to use site. But after a while I had to change host. On the new server when the members fill out form and then session ends. According to my tests when i delete $var = $_POST['variable'] ; session continues as it should be but this time i can't import variables value ... $_POST method usage changed ? because there is unneeded or hidden form fields variable $_POST imports . Please note that I am using a new version of apache server now.