Z600 new Secure Boot Certificate

[Challenger392]

Thank you for the feedback on your Dell. 

Sure is interesting. 

Was this Dell a existing Windows intallation that was upgraded or did you do a full on clean installation of Windows 11 24H2 then up to 25H2? 

Ya possible something going on with this one Z600 I tried with.  I'm coming in to another Z600 that is already with in the home and have already got another Z640 in house and made it staged and ready for the Z600 owners Win11 installation. Got zero issues after imaging Win10 over to a slave drive, got the drive crossed over from MBR to GPT. Z640 supports both Legacy and UEFI BIOS options which I already new with my two I've already been using for past few years. Got there drive installed with Win 11 25H2 directly and then just the other day installed the 6/2026 security feature update successfully. System is working fine so far. Just have to make completed configurations and make sure it's all working well, image it then put it in place of the old Z600. 

When I get back from a family reunition next week, will find some time with this 2nd Z600 and do some installation testing and see if same issue appears on this 2nd one. If so, will try and find the logs and see if they can report or show anything.

Possible I'm not follwing something. Been taking notes and making process documentation to follow. 

Just very odd that the base Win11 25H2 installation works on the Z600. But once these feature updates are applied, it breaks the boot sequence. All boots correctly until one of these security updates is applied. Hoping to find what is broken here if I can. I'll try installing Win11 25 H2 and go directly to the newest 6/2026 update and see if same thing happens. Most likely it will. Will try your process again as well, 24H2, 25H2 enablement, then update from there. 

[Paul_Tikkanen]

You're very welcome.

I clean installed W11 24H2 on the Dell around this time last year.

Then I gave it back to my son and it took him this long to get around to setting it up as a spare PC.

He did the updates to 24H2, and then I gave him the W11 25H2 enablement package file to do an in-place upgrade to 25H2 which ran without a hitch.

Yes, that is very strange that you can get W11 25H2 running fine on the Z600 until you get to that one security update.

[Challenger392]

Ok so I managed to test another z600 workstations PC out. 
Got later Win11 25H2 imaged on USB drive with recent updates, MBR with and without CA2023 Certs being on the USB drive. RUFUS built USB Drive. 

After getting thru the initial blue screen installtion process, PC reboots and checks for USB then Hard Disk drive. It stops right here with a blinking cursor only and fails to continue to boot to continued the installation process. All Stop Here.

I checked both PCs and both have same PCB FAB Rev 1.0 Motherboards and BIOS v3.6.1 which was last version released by HP back in 2018.

Something with newer Win11 25H2 and updates starting round April 2026 has changed something and now breaks the boot sequence on HP Z600 Workstation PC's that don't have UEFI and just MBR Legacy BIOS. Even though the CPU supports SSE4.2. I wouldn't put it past MS to have done this change on purpose. However, we may not ever know. All other HP Workstations PCs I have that do have some form of UEFI support in the BIOS and support SSE4.2 and don't support newer version of the 2023 security certificates, have been loading and updating windows updates now past July 2026. Now wondering when this may change.