I've spent hours today resolving issue described in Title of this thread.
I decided to run NT7 on my older computer that I didn't use for like two years. I run NT7 on this computer before and it worked great. But today I tried to run NT7 (still installed on that computer) and that error message appeared ("NinjaTrader is having problem connecting to its' licence servers....").
I updated NT7 to the latest version >> didn't worked, one-two re-installations >> didn't work... I had no idea what was wrong...
And guess what? Suddenly I realized Date & Time was set to 2002! And that was it! When I changed date and time to correct value everything works.
Maybe this will help someone some day...
Cheers!