An internet search shows a proximate meaning for your error messages:
Sip 484 Address Incomplete
This response indicates that the server received a request containing an incomplete address.
Sip 404 Not Found (User not found)
The server has definitive information that the user does not exist at the domain specified in the Request-URI. This status is also returned if the domain in the Request-URI does not match any of the domains handled by the recipient of the request.
These messages indicate there is some problem with the dialing. To troubleshoot I would start by looking at the
Status --> Call History
to see what was dialed, if what was dialed looks reasonable, and if not what you dialed try searching for what possibly could have messed it up. Probably something to do with the Phone Port DigitMap or Phone Port OutboundCallRoute if you modified the default settings.