After a backup has been missed or skipped, on opening the agent the user is presented with the Account Wizard for creating a new account (or reconnecting to an existing account). The account settings appear to have been lost.
The backup agent is unable to save its own settings files (connection.properties), or the settings files have been quarantined, usually as a result of either a full disk or an issue with antivirus software.
If the problem is a full disk, clear space on the disk before attempting to reconnect to the backup account.
If the problem is antivirus, add the recommended antivirus exclusions to the agent before attempting to reconnect.
You can find the steps for reconnecting to an account here.