First install the Lync resource kit from here Download
Second there is a Lync Server Logging Tool in the start menu of the Lync server
Start it and make sure to select S4,SIPStack & UserServices for now, you could also select all flags, then just hit start.
Now log in or try to make a call or reproduce the problem that you experiencing.
Then hit stop logging. And click Analyze Log Files
Now if we didn’t install the resource kit earlier we would get a notice that we don’t have it installed when we now click Analyze Log Files. But if it is installed snooper will open when you click Analyze in the window that popped up.
The first window is new in Lync snooper tool and if you click on the Messages tab you will recognize yourself if you ever played with the OCS 2007 R2 snooper tool.
Now if you have any problem it will for sure show up in red here and in most cases you can just google it and find a solution or post it in the forums to have someone help you.
One more short tip is to enable logging in the Lync client, then look in the %userprofile%\tracing and just open it with snooper and you can use the excellent tool for that to.
For info on how to troubleshoot a OCS 2007 / R2 server refer to my post