SIP 401 - Unauthorized usually means that the request requires user authentication.
This error message is returned by the SIP server, only your PBX administrator or VoIP provider know for sure why this reply is being send to the softphone.
The most likely reasons are that something is wrong with the SIP username, password or authentication username in the SIP account options.
Another reason for the provider to return this error message could be if you are trying to register your VoIP account on multiple devices at the same time. Some VoIP servers will reject multiple registrations. If you need to use your phone number on multiple devices simultaneously, you can always contact your VoIP service provider or PBX administrator.
If none of the suggestions above help, please contact your VoIP provider for further assistance.