The Lync Connectivity Analyser is a handy tool for troubleshooting some issues – and is available from http://www.microsoft.com/en-au/download/details.aspx?id=36535
Recently i found it was crashing on startup, seemingly from a recent patch.
Uninstalling KB2840642v2 (.net framework 4.5 update) made it work again for me.
Obviously this might not be an issue for everyone…. either way, i hope the patch gets updated or the LCA gets updated soon-ish.