[eluser]Rick Jolly[/eluser]
CI sessions store all data client-side in a cookie. IE will only allow 4kB per cookie and 20 (now 50) cookies per domain. If you need to store more information in the session you can use native sessions or one of the session libraries in the wiki. Native php sessions only store the session id on the client, and all the session data is stored in a file on the server.