Windows 8.1 and boot camp 5.1 - windows cannot verify product key

I am trying to install Windows 8.1 OEM using boot camp 5.1 and all works okay until after which boot camp re-starts the laptop and starts off the windows 8.1 installation routine automatically and I am asked to put in the product key. I enter the product key correctly but get the error message saying that the product could net be verified and so the installation will not continue past that point.

I have started off the Windows 8.1 installation on a spare computer to test the product key and all is okay but it won't work through boot camp.