Another Update: I had to do a iso in place reinstall to get my system back to operation. The update corrupted my Outlook program and a few other things.
Latest Security Update KB5079473 (26200.8037) Fails to Install
![](data:image/svg+xml, %3Csvg xmlns='http://www.w3.org/2000/svg' height='64' class='font-weight-bold' style='font: 600 30.11764705882353px "SegoeUI", Arial' width='64'%3E%3Ccircle fill='hsl(112.00000000000001, 45%, 20%)' cx='32' cy='32' r='32' /%3E%3Ctext x='50%25' y='55%25' dominant-baseline='middle' text-anchor='middle' fill='%23FFF' %3EDG%3C/text%3E%3C/svg%3E)
Doug Golden
75
Reputation points
Have downloaded and attempted to install multiple times with continued error 0x800f0991. What should I do to fix this problem?
Windows for home | Windows 11 | Windows update
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Doug Golden 75 Reputation points
2026-03-11T15:28:05.03+00:00 The issue self corrected this morning and was able to install without using any of the options below.
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![](data:image/svg+xml, %3Csvg xmlns='http://www.w3.org/2000/svg' height='64' class='font-weight-bold' style='font: 600 30.11764705882353px "SegoeUI", Arial' width='64'%3E%3Ccircle fill='hsl(115.19999999999999, 60%, 21%)' cx='32' cy='32' r='32' /%3E%3Ctext x='50%25' y='55%25' dominant-baseline='middle' text-anchor='middle' fill='%23FFF' %3EDK%3C/text%3E%3C/svg%3E)
dilkhush kumar jha 10 Reputation points2026-03-12T18:10:58.81+00:00 I am getting this error Install error - 0x80070002. Not able to install anything and having no brightness control options.
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![](data:image/svg+xml, %3Csvg xmlns='http://www.w3.org/2000/svg' height='64' class='font-weight-bold' style='font: 600 30.11764705882353px "SegoeUI", Arial' width='64'%3E%3Ccircle fill='hsl(204.8, 70%, 29%)' cx='32' cy='32' r='32' /%3E%3Ctext x='50%25' y='55%25' dominant-baseline='middle' text-anchor='middle' fill='%23FFF' %3ESG%3C/text%3E%3C/svg%3E)
Sandra Goulet 30 Reputation points2026-03-12T19:32:12.9133333+00:00 When installing KB507473 I am getting the same error Install error - 0x80070002. I have tried numerous fixes and nothing works. Only having this issue on one machine.
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![](data:image/svg+xml, %3Csvg xmlns='http://www.w3.org/2000/svg' height='64' class='font-weight-bold' style='font: 600 30.11764705882353px "SegoeUI", Arial' width='64'%3E%3Ccircle fill='hsl(73.60000000000001, 69%, 17%)' cx='32' cy='32' r='32' /%3E%3Ctext x='50%25' y='55%25' dominant-baseline='middle' text-anchor='middle' fill='%23FFF' %3EJ%3C/text%3E%3C/svg%3E)
JardaB 20 Reputation points2026-03-12T22:22:34.45+00:00 The KB5079473 update did not complete; it reported a problem, twice returning the system to its previous state and restarting. Fortunately, the system booted up, and the Update indicates a failed update with an offer to repeat.
winver 26.200.7840 --- Avast
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![](data:image/svg+xml, %3Csvg xmlns='http://www.w3.org/2000/svg' height='64' class='font-weight-bold' style='font: 600 30.11764705882353px "SegoeUI", Arial' width='64'%3E%3Ccircle fill='hsl(137.6, 75%, 23%)' cx='32' cy='32' r='32' /%3E%3Ctext x='50%25' y='55%25' dominant-baseline='middle' text-anchor='middle' fill='%23FFF' %3EBA%3C/text%3E%3C/svg%3E)
brian agne 25 Reputation points2026-03-13T13:36:00.9033333+00:00 I have been trying since 3/10 and it has not self-resolved.
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brian agne 25 Reputation points
2026-03-13T14:58:21.2+00:00 After running/retrying Windows Update says that it is 100% downloaded, and then quits at 100% installing. Shows that the update failed, error 0x800f0991Windows 11 (OS Build 26200.7840)
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Doug Golden 75 Reputation points
2026-03-13T15:24:15.46+00:00 FYI - It did not last long and I was forced todo a complete in place ISO update. Also had to fix Outlook issues and some other stuff..
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![](data:image/svg+xml, %3Csvg xmlns='http://www.w3.org/2000/svg' height='64' class='font-weight-bold' style='font: 600 30.11764705882353px "SegoeUI", Arial' width='64'%3E%3Ccircle fill='hsl(243.2, 71%, 33%)' cx='32' cy='32' r='32' /%3E%3Ctext x='50%25' y='55%25' dominant-baseline='middle' text-anchor='middle' fill='%23FFF' %3EIB%3C/text%3E%3C/svg%3E)
Igor Bozhinovski 0 Reputation points2026-03-13T15:43:40.8666667+00:00 On my side this was fixed by running the following commands on CMD as admin to empty the system reserved partition:
mountvol Y: /scd /d Y:\EFI\Microsoft\Boot\Fonts
del *.ttf
After emptying the system reserved partition and retrying to install the update it should update successfully.
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![](data:image/svg+xml, %3Csvg xmlns='http://www.w3.org/2000/svg' height='64' class='font-weight-bold' style='font: 600 30.11764705882353px "SegoeUI", Arial' width='64'%3E%3Ccircle fill='hsl(246.4, 86%, 33%)' cx='32' cy='32' r='32' /%3E%3Ctext x='50%25' y='55%25' dominant-baseline='middle' text-anchor='middle' fill='%23FFF' %3EM2%3C/text%3E%3C/svg%3E)
MarkN-2486 10 Reputation points2026-03-13T18:44:13.66+00:00 I'm getting a 0x80010002 download error and cannot get arround it.
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![](data:image/svg+xml, %3Csvg xmlns='http://www.w3.org/2000/svg' height='64' class='font-weight-bold' style='font: 600 30.11764705882353px "SegoeUI", Arial' width='64'%3E%3Ccircle fill='hsl(38.4, 91%, 13%)' cx='32' cy='32' r='32' /%3E%3Ctext x='50%25' y='55%25' dominant-baseline='middle' text-anchor='middle' fill='%23FFF' %3EBH%3C/text%3E%3C/svg%3E)
Burt Hooker 10 Reputation points2026-03-13T21:22:15.83+00:00 I'm having the same issue on a brand new Dell computer I'm setting up for one of my users. This update will not install either via Windows update or manual download. I've restarted the suggested services, set them to automatic, ran SFC, ran DISM, cleared the update cache, and downloaded/ran the install from Microsoft for Windows 11 Pro 25H2. Nothing works. Brand new machine...
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John L 10 Reputation points2026-03-14T10:37:45.54+00:00 Why is there an issue EVERY MONTH these updates come down to us??? EVERY MONTH these updates cause issues. What the hell, Microsoft????
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![](data:image/svg+xml, %3Csvg xmlns='http://www.w3.org/2000/svg' height='64' class='font-weight-bold' style='font: 600 30.11764705882353px "SegoeUI", Arial' width='64'%3E%3Ccircle fill='hsl(134.4, 57.99999999999999%, 23%)' cx='32' cy='32' r='32' /%3E%3Ctext x='50%25' y='55%25' dominant-baseline='middle' text-anchor='middle' fill='%23FFF' %3EDS%3C/text%3E%3C/svg%3E)
Don Sellick 0 Reputation points2026-03-14T16:59:00.1933333+00:00 I had left my 2 month old Dell PC running ( using Bitdefender AV) after a session but returned to find it displaying a message on screen saying it was preparing to run Automatic Repair. I went through that process and it said it couldn't be repaired and couldn't connect to network. See logfiles\Srt\SrtTrail.txt . Using my System Restore disk it kept suggesting the only solution was to reinstall Windows and lose all of my files. After multiple attempts I was finally able to restore my PC to working condition without losing any files. However it still will not load the update file - again after multiple attempts of trying. What is going on here? Almost new PC, Top level AV, always updated but still problems!
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Answer recommended by moderator
Doug Golden
75
Reputation points
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![](data:image/svg+xml, %3Csvg xmlns='http://www.w3.org/2000/svg' height='64' class='font-weight-bold' style='font: 600 30.11764705882353px "SegoeUI", Arial' width='64'%3E%3Ccircle fill='hsl(288, 23%, 37%)' cx='32' cy='32' r='32' /%3E%3Ctext x='50%25' y='55%25' dominant-baseline='middle' text-anchor='middle' fill='%23FFF' %3ESF%3C/text%3E%3C/svg%3E)
Simon Fincher 0 Reputation points2026-03-15T19:17:26.12+00:00 I tried all the various solutions and found that the in-place reinstall was the only way I could get out of the failed update loop. Everything's now updated and seems to work ok, but it took approximately two hours to get things back to normal.
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![](data:image/svg+xml, %3Csvg xmlns='http://www.w3.org/2000/svg' height='64' class='font-weight-bold' style='font: 600 30.11764705882353px "SegoeUI", Arial' width='64'%3E%3Ccircle fill='hsl(220.8, 81%, 31%)' cx='32' cy='32' r='32' /%3E%3Ctext x='50%25' y='55%25' dominant-baseline='middle' text-anchor='middle' fill='%23FFF' %3EA%3C/text%3E%3C/svg%3E)
Дария И. Иванова 5 Reputation points2026-03-17T19:14:05.31+00:00 After security update (KB5079473) (26200.8037) the network folder is not visible from my player
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![](data:image/svg+xml, %3Csvg xmlns='http://www.w3.org/2000/svg' height='64' class='font-weight-bold' style='font: 600 30.11764705882353px "SegoeUI", Arial' width='64'%3E%3Ccircle fill='hsl(76.8, 73%, 17%)' cx='32' cy='32' r='32' /%3E%3Ctext x='50%25' y='55%25' dominant-baseline='middle' text-anchor='middle' fill='%23FFF' %3ESB%3C/text%3E%3C/svg%3E)
Sean Brimigion 0 Reputation points2026-04-06T13:11:11.7366667+00:00 We also ended up doing an in-place upgrade with one of our users, jumping the device from 24H2 to 25H2. Seemed to work at first, but then the device was showing the update as being available again. Hasn't happened with a fresh 25H2 image; it seems to only affect 24H2 devices already in production. I wonder if this has been the case for anyone else?
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3 additional answers
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![](data:image/svg+xml, %3Csvg xmlns='http://www.w3.org/2000/svg' height='64' class='font-weight-bold' style='font: 600 30.11764705882353px "SegoeUI", Arial' width='64'%3E%3Ccircle fill='hsl(291.2, 41%, 38%)' cx='32' cy='32' r='32' /%3E%3Ctext x='50%25' y='55%25' dominant-baseline='middle' text-anchor='middle' fill='%23FFF' %3ERM%3C/text%3E%3C/svg%3E)
Robert Maksym 0 Reputation points2026-03-18T13:42:23.6866667+00:00 No third party antivirus. Windows 11 version 25H2 (OS Build 26200.8037). Screen shot does not work.
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Robert Maksym 0 Reputation points
2026-03-17T15:32:08.5166667+00:00 I cannot open office 365. I cannot find nor open any windows files.
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David-M 123.5K Reputation points Independent Advisor2026-03-11T12:23:28.9166667+00:00 Hi. I'm David, and I'm happy to help you.
Please clarify the following:
Do you have a third-party antivirus installed? If yes, which one?
Also. What is the current "OS Build" of your Windows 11?
- Press "Windows + R", type
winver, and click OK.
If you prefer, share a screenshot. Use the shortcut "Windows + Shift + S" to use the screenshot tool.
Be sure to censor your email address if it appears. The Microsoft Q&A is public.
I await your reply.
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![](data:image/svg+xml, %3Csvg xmlns='http://www.w3.org/2000/svg' height='64' class='font-weight-bold' style='font: 600 30.11764705882353px "SegoeUI", Arial' width='64'%3E%3Ccircle fill='hsl(281.6, 98%, 37%)' cx='32' cy='32' r='32' /%3E%3Ctext x='50%25' y='55%25' dominant-baseline='middle' text-anchor='middle' fill='%23FFF' %3ESM%3C/text%3E%3C/svg%3E)
Åsmund Møll Frengstad 5 Reputation points2026-03-12T13:27:45.34+00:00 I'm experience the same issue and no external anti virus installed.
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![](data:image/svg+xml, %3Csvg xmlns='http://www.w3.org/2000/svg' height='64' class='font-weight-bold' style='font: 600 30.11764705882353px "SegoeUI", Arial' width='64'%3E%3Ccircle fill='hsl(182.40000000000003, 76%, 27%)' cx='32' cy='32' r='32' /%3E%3Ctext x='50%25' y='55%25' dominant-baseline='middle' text-anchor='middle' fill='%23FFF' %3EDS%3C/text%3E%3C/svg%3E)
Donald Sangster 100 Reputation points2026-03-16T04:35:31.7666667+00:00 I have also had this issue and have uninstalled KB5079473 and blocked updating as it tries to automatically reinstall. The computer crashed 4 times in 24 hours, it has never done so before.
Windows version s5H2 (OS Build 26200.7840)
I do not have third party antivirus.
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Donald Sangster 100 Reputation points
2026-03-16T04:35:58.8933333+00:00 Minidump file is loaded to Dropbox: https://www.dropbox.com/t/LQwmyEej99D8u2yP
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_AW_ 68,741 Reputation points Volunteer Moderator2026-03-16T04:43:39.88+00:00 @Donald Your dump is from last September which is long before this current issue and therefore not relevant.
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