Been having similar issues here…"Ilok server isn’t running’ or something like that. Comes up with Slate, McDsp and Lexicon plug-ins here.
Strangely enough some other plugs (Altiveb) don’t seem to suffer from it.
I’ve done all the things suggested…a complete wipe of the iLok software and drivers and reinstall, and VST cache clearing…it makes no difference.
But yes, it does seem to be memory related; it only comes up on really heavy sessions.
Elicenser on the other hand has been rock solid…never had a problem with it in years.