Had a “funny” problem the other day, where a customer who I installed Lync Server 2013 for was struggling. They were experiencing that incoming calls would appear twice (two toasts) whenever simultaneous ring or Call-forwarding was enabled. Normal outbound calls to the same forwarded number was working. I set up a test account myself, but for me the Call would just terminate if sim-ring or Call-forwarding was enabled. Since my Lync running the test account was on a Virtual machine with no sound Device, I was not sure whether I could trust the results.
Debugging the logs was not fruitful, nothing related to the call flows themselves. I did note though, that there were several S4 Messages stating “Misformed SIP header” – something related to non-alphanumeric character,
From the SIP trunk provider I got some feedback that there were occasional SIP “500 Internal Server Error” messages being sent from my Mediation service.
I tried to search for other reported issues similar to mine, but found little. A colleague has blogged about Call Transfer failures on a Lync Server 2013 (http://msunified.net/2013/01/09/cannot-complete-the-transfer-in-lync-server-2013/), and although my issue was not quite what he had experienced I tried to see if Windows Update had anything important waiting for me (which was the case for him). I found one .NET 4.5 update was waiting to get installed, so I applied it and restarted.
Problem now seems to be fixed, at least I am able to transfer, forward and sim-ring. Just another strange case, I guess, but one to be aware of.