If you unchecked the box next to "remember this password in your keychain".......but it was checked previously at one time.......then there are likely different passwords that have been stored for the same wireless network name at different times, which will result in conflicts.
Try changing the wireless network name as well as the password for the wireless network. If you have had different passwords for the same wireless network name over time, this is also bound to create conflicts at some point, like possibly now.
If you are still having problems I would start all over again with a factory default reset on the AirPort Extreme and then set it up again from scratch using different device names and passwords that you have not used before.
Would also be a good idea to leave the default setting to have your password remembered in the keychain, since this is tied not only to your local Mac, but also to iCloud. You don't want different information on iCloud that you have on your Mac.
Finally, if you are using an older version of AirPort Utility, make sure that Back to My Mac is not enabled on the application.
