I know there are confusions around 32 bit and 64 bit versions of ADPREP. Windows Server 2008 R2 includes a 32-bit version and a 64-bit version of Adprep.exe. The 64-bit version runs by default. If you want to run one of the Adprep.exe commands on a 32-bit computer, use the 32-bit version of Adprep.exe. It is called Adprep32.exe. In Windows 2008 R2, it is located in the \Support\Adprep folder.