I am not worried about the flash drive itself, just want to make sure you got the image from Microsoft.
As you have done a clean install, it cannot be an image issue and I don't think it is a network issue either.
That narrows down to the key - the history and context of this key is very minimum, which is the limitation here for a thorough troubleshooting. Have you ever had the chance prior to all of this to verify the type of the key by using slmgr /dlv command?