So you've got a Windows 11 system, and you decided to skip the normal 10/2025 update (KB5066835) in favor of KB5070773, which fixes a critical problem in KB5066835 and is *supposed* to be cumulative. But when you try to install it, you get "error 1536" (or was it "error 1236" -- I forget. It did say "error xxxx" and then direct me to examine the DISM log). Examining the DISM log at c:\windows\logs\dism\dism.log , you see very many "failed hash validation" errors.

What gives? Well, the problem is that KB5070773 is NOT cumulative. You must install KB5066835 first, then install KB5070773. This is bad, since KB5070773 fixes a bug in KB5066835 that can cause your system to be irrepairable. That is, USB mice and keyboards don't work in the Windows Recovery Environment after installing KB5066835 (https://support.microsoft.com/en-us/topic/october-20-2025-kb5070773-os-builds-26200-6901-and-26100-6901-out-of-band-0f533ed7-949a-4b89-8d0f-6ee751adfcd4 ). So, if you install KB5066835 and it messes up so badly that you need to use the Recovery Environment, you won't be able to use your USB mouse and keyboard (or, it seems, any other USB device) to fix it.

Really MS should fix this bug, so that you can install KB5070773 without installing KB5066835, thus preserving USB mouse and keyboard functions in the Recovery Environment.

A person found this solution, NOT a freakin' AI bullshit generator!