If validation fails with message about invalid email, please call McNeel Sales in your region. (US 206-545-7000).
If validation fails even after Sales has reset your license, or you are prompted to enter an upgrade key and you do not have an upgrade, it is possible that you accidentally typed in your Rhino 5 License Key incorrectly. You can fix this, but you will need to delete the LIC file.
You can delete your LIC file, with Method 1 or Method 2.