Adprep "not a valid Win32 application" error on Windows Server 2003, 64-bit version

When you run the Adprep.exe that is included with Windows Server 2012 on a 64-bit version of Windows Server 2003, you receive an error that resembles the following:

You cannot run the Adprep.exe that is included with Windows Server 2012 on Windows Server 2003.

The Adprep.exe that is included with Windows Server 2012 supports remote updates of the forest and domain. There is no longer any requirement to run Adprep.exe on the existing Schema Master or Infrastructure Master domain controllers.

To update your domain, follow these steps:

1. Install Windows Server 2012.
2. Run the Adprep.exe that is included on the Windows Server 2012 installation media in the following location:
   \support\adprep
3. Use the arguments that you tried to use when you encountered the error that is described in the "Symptoms" section. For example, use the following arguments:
   • /forestprep
   • /domainprep
   • /rodcprep
   • /gpprep

Windows Server 2012 Adprep.exe also removes the requirement to join a domain. You can use the /Forest, /Domain, /Userdomain, and /Password arguments to remotely update forests and domains even from a workgroup as long as you have the correct Domain Name System (DNS) name resolution. Also, just installing and configuring the first Windows Server 2012 domain controller into a forest runs the preparation process automatically, and in this scenario, you do not have to use adprep.exe.

This behavior is by design.