Exchange connection down

So when this error occurs to check the status of Exchange Web Services (EWS) launch outlook and try to schedule a meeting, if you can see the calendar availability of people you are trying to schedule a meeting with the EWS is ok

So this will tell you if you have a try Exchange connection error, if you are able to see other peoples schedule through outlook, I would suggest you run a trace using STRACE and HTTPReplay to see if any error are being presented via the EWS.

I have a blog post about using STRACE and HTTPReplay here: http://myucthoughts.blogspot.com.au/2012/06/strace-and-httprelay.html