You may get
A referral was returned from the server. when launching Digitally signed applications like Mumble on windows.
This is normally caused by the Digital Signature expiring. You can check that this is the case by doing this here:
and then going to
As you can see this signature out of date. If you see this in the mumble case, its normally a good sign (no pun indented) that you need to update Mumble.