Now KB5015814 won't install

CORRECT. What I was paid to do before I retired (IT Manager) was to keep the systems running on a daily basis. I can assure you that I didn't have

time to look deep into problems but rather find quick fixes and workarounds to problems to keep the operation going. And I would pass along

issues like this and others to people/companies who's business it is to deal with these higher knowledge issues. Now I'm just a old retired guy...

Excuse me I gotta go mow the lawn (And scoop the dog poop)...Oh the indignity!!!

My PC got 8GB RAM...

I Had this problem on two pc's.

On the first pc the solution was to disable malwarebytes briefly:

Then under Turn Windows Features on or off turn off .Net Framework 3.5 (includes .Net 2.0 and 3.0). If that won't remove then the solutions gets more complitcated and I'll get to it in a bit.

Try installing the KB5015814 update through windows update, if that fails download the update from the Microsoft site. I had already downloaded the solo update for KB5015814 so I never got to try it again using windows update. I tried the solo update before trying to remove the .net 3.5 stuff and it failed. Once I did remove it the solo install did install the solo KB5015814 and I enabled .Net 3.5 framework again. I was trying the removing of the .net 3.5 stuff since this patch seems very related to that. All I can figure is both pc's had some sort of damage to the .net 3.5 install. Removing it on my first pc did the trick, but the second pc had a bigger problem.

The above didn't work on my other pc. The pc could not remove .Net Framework 3.5 (includes .Net 2.0 and 3.0) and I could find nothing that would fix it to be removed or fix its install.

I turned to installing windows 11 over my current windows 11, hoping doing this would fix the .Net 3.5 install. Trying to remove it gave a catastrophic error. I used the Create Windows 11 Installation Media to create an install usb for my pc. Create the usb drive. Run the setup from within Windows 11. Make sure to pick to keep your setting and apps. Make sure you disable your internet on the pc. You need to make sure windows doesn't try to install update that will cause a problem. I forgot to disable my internet the first time and it failed and rolled back to what I had causing me to remember that I should have disabled my internet. After my pc did install the over install of windows 11 I used the solo install for KB5015814, not bothering to remove the .Net 3.5 stuff. It probably would have installed using Windows update, but since I had the solo install I went with that. (The solo install seems to take a while so just wait.) This install went well and finished fine. Installing Windows 11 over Windows 11 seemed to have fixed the problem with the .Net 3.5 stuff, which is why I did an install over an install. Which is what I was hoping would happen.

Good luck people. I hope just being able to disable malwarebytes and remove the .net 3.5 stuff is all you have to do. The other way takes a long while.

(I suppose for Windows 10 you would be using Create Windows 10 Installation Media to do this on a Windows 10 pc)

Tried that and still gets to 25%, then flicks to 100% and says fail error 0x8000ffff

Thanks for that but you do realize the average PC user would have no idea what you did or how to do it. I doubt most users even know if this update failed to install for them. Unfortunate but this will take MS to fix in the long run.