Migrate secondary DC from WinSrv 2008 R2 Std to WinSrv 2012 R2 Std in place

Hi, 

I have 5 DC in three different networks, and now I try to update a secondary DC from Windows Server 2008 R2 sp1 to Windows Server 2012 R2 Std.

Domain and Forest functional level are: Windows Server 2008 (not R2)

All DC are VM on Microsoft Hyper-V.

I attached the Windows Server 2012 ISO file to the CD on the secondary DC, and I try to run the command from command prompt run as administrator: 

d:\support\adprep\adprep /forestprep

But I receive a popup with this error:

D:\support\adprep\adprep.exe /forestprep is not a valid Win32 application

And in the command prompt I see the error:

access is denaided.

The user that run the command is member of: Domains Admin (principal), Schema Admin and Enterprise Admin

All DC are Windows Server 2008 R2 sp1 x64 

Thanks for the support.

Marco