I was playing around with Call Via Work today, bolting into a CUCM instance on Hyper-V , and got this error.
So I was head scratching for a bit thinking this will work. I bing'd the error and hit a great article by skypeadmin Anthony Caragol on the error. It was basically I didn't have my external web service URL available when I was running my lab (as I was just doing internal stuff).
Have a read of the article, it is great http://www.skypeadmin.com/2015/06/09/quick-tip-call-via-work-call-controls-are-unavailable/
Because my lab runs a split DNS zone for my sip domain, and as I didn't have the ability to route internal traffic out to my proxy and back in (to get to the pool external webservice name for UCWA), I decided to create a new VIP on my internal HLB to pass thru traffic to my FEs for internal traffic. So I created a new VIP, listened for traffic on 443/80 and mapped through to 4443 and 8080. Then I just added a new internal A record for external webservice name.
Hopefully no one else hits the issue, a massive thanks to Anthony!