Custom Win11 Pro 25H2 ISO fails to install unless old setup is used

At first, I thought there was an issue with the autounattend.xml or unattend.xml - but removing both files from the ISO build resulted in the install still failing. So, on a hunch, I tried switching to the old version of setup (obviously without the autounattend.xml or unattend.xml) - and the install worked flawlessly.

The same issue is occurring in a VM or on a physical PC (both an older Dell that meets Win11 requirements and a newer Lenovo which also needs requirements were tested).

Testing shows that the install reaches around 10% on the "Installing Windows - your PC may reboot several times" screen and then the "Windows 11 failed to install" popup appears. There are no further details given.

I either need to fix the issue that is causing it to need the old version of setup - though I have no idea what that issue might be - or I need to figure out how to force the old setup through autounattend.xml as we are going to be reimaging all of our public access computers within the next couple of weeks and the thought of having to run setup manually is giving me a serious headache. Going back to a working 24H2 autounattend ISO then having to manually update to 25H2 is equally undesirable. We have around 30 PCs to image within a matter of days.

The install.wim is built according to the tutorial on the Win10 forums for creating an ISO from an existing PC, just like every install.wim that I have built since for the past 7 or so years. And, as mentioned above, it works perfectly if the old setup is selected during a standard manual install but never with the "new" setup.

My build PC is also running Win11 Pro 25H2 and I uninstalled my existing then reinstalled the most current version of the Windows Deploying and Imaging Environment.

Suggestions?

The newer ("Modern") Setup client for 24H2/25H2 tends to fail on some specific conditions:

If you can't figure out what new Setup is annoyed over, you can easily force legacy Setup to run by updating your boot.wim.

Mount the boot.wim (for example, from D:\path\folder), and apply a reg change.

MS has never acknowledged why a change was made in 24H2, nor provided any docs on what to do differently. New Setup is required because Windows is treating every clean install as an "upgrade", in so far as to create an empty Windows.old to make Setup think it's doing an in-place upgrade.

@DC_ECL, I have run into the same issue that you did in the past. In my case at least, this was always the result of not having updfated EVERYTHING. In other words, your image should be updating Win RE, Win PE, and the install.wim. The Safe OS and Setup dynamic updates should also be included.

If you need more details, please let me know.

garlin said:

The newer ("Modern") Setup client for 24H2/25H2 tends to fail on some specific conditions:

- Didn't assign a Recovery partition (old Setup doesn't require one)​

​

- When using a sysprepped image, which includes a Windows.old folder (just remove it), or some type of custom change that annoys new Setup. A sysprepped image that always worked before may mysteriously break under 24H2/25H2 without explanation.​

If you can't figure out what new Setup is annoyed over, you can easily force legacy Setup to run by updating your boot.wim.

Mount the boot.wim (for example, from D:\path\folder), and apply a reg change.

Code:

DISM /Mount-Wim /wimfile:D:\path\folder\boot.wim /index:2 /mountdir:C:\Mount
reg load HKLM\TEMP C:\Mount\Windows\System32\config\SYSTEM
reg add HKLM\TEMP\Setup /v "CmdLine" /t REG_SZ /d "X:\\sources\\setup.exe" /f
reg unload HKLM\TEMP
DISM /Unmount-Wim /mountdir:C:\Mount /commit

MS has never acknowledged why a change was made in 24H2, nor provided any docs on what to do differently. New Setup is required because Windows is treating every clean install as an "upgrade", in so far as to create an empty Windows.old to make Setup think it's doing an in-place upgrade.

Click to expand...

Registered just to show my thanks to this amazing response. I've been pulling my hair out all day trying to resolve this issue in so many different ways and this is what finally done it for me. I shall name my first born garlin to show thanks. I am now curious what about my WIM was causing the new setup client to fail but for now I'll settle on the old setup working

or I need to figure out how to force the old setup

Click to expand...

one way is to put winpeshl.ini in boot.wim image 2 \windows\system32

winpeshl.ini


mounting not needed. Last time I looked, installation media boot.wim is not read-only, so winpeshl.ini can be dragged in using 7-zip gui in a couple of seconds