It is possible for your organizer to set up a login in the app or online planner that authenticates against a 3rd party system such as the registration vendor or a member database system. To minimize server load on these external systems, your authentication is cached for 6 hours after a successful login.
If you have changed your password more than 6 hours ago, simply log out of the app and log back in with your new password. If you receive an authentication error, it may not yet be 6 hours - simply wait a couple of hours and try again. Your native apps will continue to work since your schedule information, search, adding/removing sessions, reminders, taking notes, etc. all work offline.
If you must log in asap, please contact the organizer.