According to the support, this is not the normal behavior. They are sure that the key should work on the system without a clean install. I'm suspecting this too but it seems equally strange that two different Microsoft support technicians made the same error... I'll give this problem another few days and I will try reinstalling.
I created a restore point before issuing those commands. I tried with a clean install and I'm still getting the same error on different machines. The key must be for a different edition or I'm one of the unluckiest persons installing Windows. It's strange that the technician didn't catch it. Just to be sure I will download and test the different versions of Windows enterprise the key could be for. The most probable suspect is the LTSB. I will keep you updated.