How to solve Windows cannot read the setting from unattended answer file

When it appears the command prompt digit notepad c:\autounattend.xml
You have to search the string <ProductKey> and below this insert a new line that contains the string
<Key></Key>
You don't have to insert a code, only the tags.
Save the file and relaunch manually the command X:\Windows\Hpssbem.exe again
The installation will end fine.