Front and back end sessions are set to timeout after 15 minutes and 30 minutes of inactivity respectively. After a session times out it is necessary to log back in. Whilst this can occassionally be irritating, it is for your security. If you unexpectedly get the message "You are not authorised to view this resource. You need to login." it is likely that your session has timed out. For certain modules your front end session can timeout whilst you are logged into the back end. In this instance it is necessary to logout of the back end, log back into the front end and then log back into the back end.