OK, so I got the cookies to work (long story). BUt now I face a new problem.
From one page I do a user authentication against a MySQL database. If it is successfuly I show the restricted page. I set a cookie that I will reuse to see if the user is logged in still (in another area). The problem is, if you change from the restriced page to an non-restricted page, then hit the back button to go back to the restricted page, I get the "Page Expired" message and I have to reload.
I am not setting any Cache-Control headers at the moment. Is there anything else I should check?