Norton Antivirus Error: 8506, 421 encountered and unable to remove

Good day,

Recently I experienced an error with the Antivirus which purchased online. This error appears everytime when I try to run the Antivirus software which it does not start the software or it pops up after around 5 minutes of using the PC. Initially I followed the support web site to download the Norton Removal Tool, remove the software, restart and reinstall the Norton product but the error still appears although there is no problem encountered during the download process. I then tried to use the Norton Power Eraser to scan for risk through the rootkit scan but still it does not remove the error.

I even tried to remove the software again and download through Norton backup but it seems like Norton failed to verify and recognise my product code. I am not sure at this point what else I can do (please see attached). Appreciate all help from the community and support to advise on how to remove the error and to verify my product code (VCVVTYD9KDD......), thank you. 

Rgds

qmm73