If you are getting the error message "Wrong password for registered users, please try again" — this means that the Username that you are trying to connect with was already registered on the server, and you don't have the matching certificate for that registered account.
This problem commonly happens when someone re-install their Windows operating system and forgets to import their old mumble certificate. There are three ways that this issue can be resolved:
Method 1: Import your old certificate
The best option if you still have a backup of your old certificate. To import your certificate click on "Configure → Certificate Wizard". Select the option Import a certificate and then follow the wizard to find your old certificate.
See this guide how to export and import your mumble certificate.
Tip: When you install Mumble, an automatic backup of your certificate was saved to your Documents folder, under the name "MumbleAutomaticCertificateBackup.p12". If you haven't created a new certificate since instaling Mumble, this should be your current certificate backup.
Method 2: Use a different Name
Connect to the server using a different username (Simply add numbers to the end of your name e.g. Yourname1234, an administrator can then quickly rename it later on for you) this will allow you to get back on the server right away.
Method 3: Delete the old registration
Ask one of the users on your server who have administrative access to deleted your old registration. They can do this by clicking on the "Server → Registered Users", and then highlighting your name and clicking the "Remove" button.