Start Session isn't working in Windows desktop client

Since the latest client update on my Win 10 PC (zohotray.exe 1.0.2.7 23/5/16) I can't Start Session. Nothing happens in the window when I click. It works ok when you right-click the system tray icon, bottom right, and choose Start Session there.

I've tried uninstalling and reinstalling. Any other thoughts?

Thanks, Mike.