I ran across a weird problem the other day. After installing Unity, it registering with CallManager and everything looking good, Unity either would not answer calls at all (phone just rings when trying to call voice mail) or it would answer then immediately drop the call. The Windows APP log showed a bunch of MIU errors for each failed call attempt.
To make a long story short, I found that when logged in to the Unity server via RDP using the "/console" switch (mstsc /v:<ip address> /console", it causes the problem. As soon as I log out of the console session, Unity works fine. Logging in to a "normal" RDP session, physically logging in to the console, or logging in through the server's iLO port does not cause this problem.
Just for grins, I tried it on another Unity server that's been up and running with no problems for about 5 years and the exact same thing happened.
What is it about the "/console" switch that causes the problem? Not that it's a big issue because the server is working fine. I'm just really curious about this.