Windows PE error, using Windows 8 ADK
I am trying to build a PE iso, ran into this problem.

Running:
Windows 8 Professional x64
Windows Assessment and Deployment Kit (ADK) for Windows 8

Command Prompt Output:

C:\Program Files (x86)\Windows Kits\8.0\Assessment and Deployment Kit\Windows Preinstallation Environment>copype Creates working directories for WinPE image customization and media creation. copype { amd64 | x86 | arm } <workingDirectory> amd64 Copies amd64 boot files and WIM to <workingDirectory>\media. x86 Copies x86 boot files and WIM to <workingDirectory>\media. arm Copies arm boot files and WIM to <workingDirectory>\media. Note: ARM content may not be present in this ADK. workingDirectory Creates the working directory at the specified location. Example: copype amd64 C:\WinPE_amd64

When running command: copype amd64 S:\WindowsPE I receive:

ERROR: The following processor architecture was not found: amd64.

Did you try to run the PE command line as Administrator? 

Hi,

I suggest you reinstall WAIK and try again. The architecture amd64 is missing.

No, I am using Windows Assessment and Deployment Kit (ADK).

WAIK applies to Windows 7 / Server 2008, ADK is the updated version of WAIK

You have to reinstall the ADK because AMD64 is missing on your installation. Otherwise, you can build a x86 PE, because it works to capture x64 images as well. 

Outstaning find.  Thanks wjsorensen.

Anybody that experiences this issue, please follow the instructions posted here, as they will fix the issue.  *Side note, that if you install the ADK into a different directory, other than default - be sure to update these two lines in the cmd:

set SOURCE=C:\Program Files (x86)\Windows Kits\8.0\Assessment and Deployment Kit\Windows Preinstallation Environment\%WINPE_ARCH%
set FWFILESROOT=C:\Program Files (x86)\Windows Kits\8.0\Assessment and Deployment Kit\Deployment Tools\%WINPE_ARCH%\Oscdimg

Update them to wherever ADK has been installed (if not default).  - And please share the love for  wjsorensen by "upvoting" him if the same solution worked for you.

I had the same issue. I was being a n00b and not using Deployment Tools Command Prompt.