Windows 11 25H2 - Cannot mount with DISM?

[DavR]

I'm just trying to prep our Windows 11 image for deployment over the summer holidays, but for some unknown reason, I can't get DISM to mount the install.wim from the 25H2 ISO for editing - has anyone else had trouble with this?

 

I'm getting error 5 Access Denied, which it very much is not. This is with a fresh ISO downloaded from Microsoft, both the June 2026 and September 2025 ISOs are doing the same thing. I can load my 24H2 install.wim fine, so it seems to only be the 25H2 version that's the trouble.

 

I did wonder if it was the secure boot certificate thing, but, the PC trying to load it is up to date with the 2023 certs, so I'd think not.

 

I know editing the wim is out of fashion now, but there are a few bits that I do prefer done in the image. Any ideas or advice gratefully received!

[DavR]

False alarm - I was able to mount the image with DISM, but, I had to be on a device running 25H2 to do it.

 

I feel like this has come up before. Maybe next year I'll find this thread before getting stuck on it again 😂