"Match Ip to Session" is a security setting which, when enabled, requires that the session ID used to access the administration matches the operators IP address used when logging into the admin. This is to prevent users who follow referer links clicked on in the "data" tab that have the session ID in the query string from gaining access to the admin. However, the downside in enabling this is that operators with dynamic ip addresses will not be able to log in.

"Use PHP Sessions" when enabled. use PHP sessions for the operator logging in rather then just using cookies.