I have been fighting this for some time. I can longer open projects that  have Slate iLok products in them (and that's all of them for about 3 years running). I get an iLok authorization issue popup (app not running - but it is), followed by popups for plugs not being available (they are in exact location the error says they aren't and have been scanned and show up in VST manager). At that point, Sonar loads the last screen, but goes unresponsive before the engine starts.  It's so odd because when projects would load, some Slate plugs wouldn't load, some would. Open project again, the opposite plugs would load/not load. See pic. Every project, every time... I uninstalled/reinstalled and even updated to Manchester to see if it would help - no love.

Hi. I only have the free Revival plugin from SS, but I have not had any issues with it. So sorry if this is obvious.
Is your iLok up to date? Did you do an upgrade to Win 10, or a fresh install? Is the iLok connected to an USB2 port, and not USB3?
Best of luck.

I did a clean install 3 weeks ago. All worked. I have no clue how this started. I uninstalled/reinstalled the iLok Manager, the Gobbler app, D/L'd and reinstalled the bundle.
 
Ipm'd Steven Slate. In keeping with his loyalty, asked for my phone number. Paul for support called me, and remotely fixed the problem in 10 minutes. I am up and running again!
 
Thank you so much, Steven Slate, Paul and Sonar forum - all always ready to help!!

Glad you got it figured out Can you share the solution, in case someone else finds themselves in the same situation?
All the best.