Windows update fails to install 2021-07 Cumulative Update for Windows 10 Version 21H1 for x64-based Systems (KB5004237)

Have to agree with your statement regarding MS deployment quality control. Although, there is the thought that Windows needs to work across an almost infinite number of HW combinations across many years of component evolution.

Having said that, "The source could not be found" implies that the file is just not there. That suggests that explicitly specifying the source file from a known good source (.iso) might solve that problem. Here's a link to a description from this website that describes the process. That's also the syntax I borked previously but now it's relevant ;).

https://answers.microsoft.com/en-us/insider/forum/all/how-to-repair-your-system-files-using-dism-and-sfc/1021b42a-09ff-41a0-a95a-48f3ee3ae699

You'll need an iso Windows source that's relatively recent or you'll need to download one.

Hi. I do not use Windows Defender - only Norton AV and its firewall.

That may be the case, the windows update can become problematic any time.
If you’re using Windows Defender do the virus definitions update?
Try Right click on start & choose powershell with admin & enter:
SFC /SCANNOW
DISM /Online /Cleanup-Image /StartComponentCleanup
DISM /Online /Cleanup-Image /RestoreHealth

I'm not sure, if you were answering me.... But, at home, on my computer with Windows 10 I use F-Secure Safe as antivirus program. On another old computer, with Windows 8.1, I use Windows Defender.

On my work, we useWindows 10, and Windows Defender...

On the computers, only running Windows Defender, the updates SOMETIMES installs through Windows Update, and other times they don't. Then, I opens Windows Defender, and takes the updates through this.

And check for updates in Windows Update, to get the failed update to disappear.

Other times, the updates for Windows Defender won't install at all... Then, I deactivate Windows Defender, and it will install.

I allways empties the TEMP-folders in Windows, so there's room for more updates to come.

Perhaps, it's time for the DISM's.......

Good evening.

I'm sorry that you went through all of this. I've spent untold hours on this as well. I appreciate everyone's input and work on my behalf. Seeing that others too have experienced it does not help from a "misery ;loves company" perspective. All that it offers, is that I probably did not screw up too much - yet.

In parallel situation with AMD and their video drivers. I thought that they could have been related, but apparently they are not.

The AMD people responded to my similar request as to why a video card update would not install. It seems that my card is now considered legacy. I'm waiting to find out if I should now ignore update prompts or stay with the version I downloaded today, while AV and FW protections were disabled.

I tried disabling protections with the WIN10 patch in question and there was no improvement, just the new error I received. : There were some problems installing updates, but we'll try again later. If you keep seeing this and want to search the web or contact support for information, this may help: (0x800f0831).

Again, thank you to all who have tried to come to my aid. Perhaps some positive results may be forthcoming.

Be well!

Your 1726 error from DISM might be related to having an anti-virus or firewall program running while running DISM.

I have invested close to another 8 hours into this today and have made no headway. I have shutdown Windows Update services, deleted the c:\windows\SoftwareDistribution and C:\windows\cbstemp folders, restarted the Windows Update services, and then tried installing this update again. Same failure.

I just tried running the DISM command that was recommended. It took ~2 hours to reach 100% and then gave this error:

Error: 0x800f081f

The source files could not be found.

Use the "Source" option to specify the location of the files that are required to restore the feature. For more information on specifying a source, see https://go.microsoft.com/fwlink/?LinkId=243077.

To say that I am disgusted with Microsoft and its low-quality software development practices is a gross understatement.