Error 6 on activating Norton Utilities Premium only in one of my systems

Have Norton™ 360 with LifeLock™ Ultimate Plus for close to 2 years already. Just this one system having trouble activating NUP and gives Error 6. Have been uninstalled and reinstall but still getting the same error. 

All my other systems in the home network are activated and working just fine.

Have done that already more than a couple of times. Same error 6 for this system. In fact, ... have also completely uninstalled and re-installed more than a couple ot times also. Same Error 6!

If you are able to get to the home screen of NUU, click on the Help ?, and then click on About Norton Utilities Ultimate and then click Change Key. Enter your key there and that should get NUU activated again.