Whenever something goes wrong, or as it shouldn't supposed to with YateClient, you can use the debugging tool provided.
For this, in Main Menu, go to Settings -> Debug Window and click:
Right now, the window in which you'll have the messages log will appear, showing the accounts you are logged into (if any):
You can turn on detail display for individual VoIP protocols (JABBER, SIP, H.323, IAX).
Screenshots are from YateClient version 4.0.