Z200/Z400/Z600/Z800 Windows 11 Boot Failure Nov 2025 KB5066835 - A Disk Read Error Occurred

[blakefrogget]

Hey vanadu, no-link super simple fix:

Grab Microsoft's "Show or hide updates" tool (just google wushowhide), run it, hide KB5066835, done.

Your Zx00 boots again in 2 minutes flat. No reinstall, no BIOS mess. Works perfectly.

https://aitoolranker.com/ 

[SDH]

Blakefrogget,

Your solution assumes the ZX00 workstation is still bootable. The fatal error we're seeing is that after update the ZX00 workstation won't even boot.

Also, note my post earlier in this thread that after a clean install of W11 25H2 and seconds after the first boot just after first connection to the internet the single KB I found that needed to be hidden was not KB5066835 and was KB5068861 instead. This might mean that earlier the "killer" KB truly was KB5066835 and that Microsoft replaced that with KB5068861 but that it still had the fatal  bug (for the ZX00 workstations) inside. I've not seen the same effect on UEFI/EFI workstations such the ZX20 and on.

[capitan_baudo]

Hello and thank you for your continued support.

I think the best thing to do right now is to continue cloning or backing up the Zx00s before doing any updates and assess whether this dual boot issue will be resolved after KB5066835 is removed.

I'm continuing to test the Z600 and Z400 to establish a stable path before using them as work machines and I'll post any further findings or results here, as you're doing. It's definitely best to suspend automatic updates, at least for now.