Session Reset Problem

hi,
I have been working on project where it has a admin area with an admin log-in page, I track the logged in user using a session variable set by a log-in function. my problem is it logs the user in and when it clicks a link on the admin panel
it kicks out the user giving the login screen again, when I had a closer look @ the problem, I noticed that, it resets the session variable in the next user page request, I have been reading few forums regarding this problem bub none provides a positive answer rather than passing the session details into the next page using the URL. has anybody come across this problem or any possible solutions except the URL passing would be thankful.

Regards.