SOLVED: SysPrep – [0x0f0070] SYSPRP RunExternalDlls:An error occurred while running registry sysprep DLLs, halting sysprep execution. dwRet = 0x3cf2

If you are trying to SysPrep a Windows 10 PC and see:

Sysprep Failure Unable to Validate Windows Installation

and then see in the log:

[0x0f0070] SYSPRP RunExternalDlls:An error occurred while running registry sysprep DLLs, halting sysprep execution. dwRet = 0x3cf2

You likely have some Win10 apps that are installed per person.  Things like the calculator and paint may be installed by default but they are installed per person and not allowed to be sysprepped.  Fortunately the fix is straight forward:

1. Open a CMD PROMPT as an admin (PowerShell does not seem to work with these commands)
2. Type Import-Module Appx and press the enter key
3. Type Import-Module Dism and press the enter key
4. Type Get-AppxPackage | Remove-AppxPackage and press the enter key

A reboot is not required so you can try your SysPrep again.