On Athena workstations, you may receive an error that says something to the effect of "Your password no longer matches your keyring" and then prompts for your a password to "unlock your keyring". This error may occur when you log in, or when you open an application that has saved password information (e.g. Evolution, Pidgin).
Ubuntu Linux uses keyrings (similar to the Keychain on MacOS) to store saved passwords and other sensitive information. This keyring is typically protected by your login password. In rare cases, it is possible for the keyring password to become out of sync with your login password. When this happens, your keyring can't be opened at login time, and you are prompted for the old password.
If you remember your previous Kerberos password, you may try to unlock your keychain with that password. There is no limit to how many attempts you may make to unlock your keychain.
If you are not able to unlock your Keychain with your previous password, you will need to delete your keyring (and lose any information stored in it) with the following command:
In Debian 11