I am having problems activating DS2018 x64 on a WIN8 platform

Clean install, I can activate the software and I get the activation link email - I can click on this and get the message 'Activation Successful' from the website. When I relaunch DS2018 (Free), I get the Check email to confirm activation dialogue box.

The troubleshooting guide for this error says

If the point above is not applicable, the recurrent prompt for activation means that the
activation is not validated locally: This is usually due to lack of permissions of User
Account/Application, as the validation of the activation involves the editing of
files/data in locations deemed sensitive under certain configurations. Contact your IT
Department to check these settings and your user account, and or any other security
application/setting that are active, and might be blocking the activation.

I am running the application as an administrator on a machine for which I have full admin privileges. Can anyone tell me what permissions need to be applied and to where. I was a very happy DS2017 user...

Thanks

Martyn