Installing an HP OEM Windows 2012 R2 Essential server as KVM Guest

I have an HP Proliant DL385p Gen8 box together with a HP/OEM installation disk of Windows Server 2012 R2 Essential.
On the iron I've installed Ubuntu Server 12.04.5 64bit plus xfce 4.1 (horrible: avoid it!) and KVM latest version available in ubuntu repository at the time of this writing (Dec2014).
The windows server is going to run as a guest over KVM. I have plenty of configurations like this perfectly working where, however, the Windows software is not OEM..
Here, a little while after the windows server installation CD boots up in the guest, it stops with the following message:"This system is not a supported platform": the hardware platform must be an HP and the actual one is not. No way.