AVG License Error

Hello McBane,
We regret for the inconvenience caused. Did you try reinstalling a new version of your AVG program to fix the issue? Thank you.

I have AVG Internet Security for 2 computers for 12 months from January 2016.  Both were installed and have worked fine until yesterday.  One computer's protection is still fine.  On the other, I now have no protection and the message is: 'AVG License Error - AVG is not able to recognise your License number'.
I've tried numerous times to re-enter the License number, copying and pasting it from your original Confirmation.  There is then an immediate message with a tick, saying 'License valid', but after a few minutes the same message comes up and I'm still not protected.  I've tried restarting the computer and that makes no difference.
Please help! 

Hello McBane,
We regret for the inconvenience caused. Did you try reinstalling a new version of your AVG program to fix the issue? Thank you.