license re-activation required, fails

I upgraded my IntelliJ IDEA Ultimate edition to 2016.2 last week and it ran fine. Got back to work on Monday and am greeted with a "license activation" prompt. All attempts to re-acquire a license from the server have failed. (see screenshot) I have deleted all my preferences and configurations, and it still fails. I don't have a proxy in play, and I made no changes to proxy settings, neither in IntelliJ IDEA nor in my OS (Mac OSX 10.10.5).

I rolled back to 2016.1.3 and re-activated the license and it worked flawlessly. I'm thinking there's a bug somewhere in 2016.2, perhaps relating to the proxy configuration settings screen.