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March 17th, 2026 22:35
Pro Max 16 MC16250, update not installed - strange message. Need help!
Hello everyone!
I am using at home a laptop Dell Pro Max 16 MC16250 purchased at the end of July 2025. There were no technical problems up to now: KB5079473 can not be installed – error 0x800f0831 each time. The Windows 11 version now is 25H2, 26200.7840 (but I am not an Insider).
After waiting 3-4 days I tried (assisted by Copilot): cmd prompt DISM, scannow, services …, restore to 26100.xxxx, windows repair. No success! Apparently DISM do not work, ISO file could not be installed “this computer is not eligible for Windows 11, recovery partition could not be found”, windows repair with an installation media – the same result. I asked for remote help first at Dell Assist, than at Microsoft. The results were the same as above.
Indications: from Dell – “reinstall everything” ; from Microsoft – “ask for help by the producer!”.
I would also like to add that the laptop has – from the very beginning – two SSDs:
SSD1 - 512 GB for the OS; This SSD was ordered right from the start and was set up by the seller before delivery, with OS installed.
SSD2 – 1 TB for the work files
NOW: I have stopped the updates for a week.
I am living in RO-Bucharest. I would be very grateful for an advice or any indication for a proper service in Romania.
Rohan furqan
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1 Message
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March 18th, 2026 03:34
That error usually means Windows is missing some update files or dependencies.
Try this (quick fixes):
Run Windows Update troubleshooter
Settings → System → Troubleshoot → Other troubleshooters → Windows Update
Repair system files (important)
Open Command Prompt as admin and run:
(edited)
BeastGamer13
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13 Posts
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March 18th, 2026 05:26
Download KB5079473 directly from the Microsoft Update Catalog (search "KB5079473"), match your x64 architecture (it should be fully same as shown in windows update), and install it offline.
CarloMax
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2 Posts
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March 18th, 2026 09:07
I am experiencing the exact same issue with two brand-new Dell PCs. Both machines are failing to install KB5079473 with the 0x800f0991 error right out of the box. Specifically, the models are:
Dell Pro Max T2
Dell Tower ECT 1250
On the very first startup, I performed all recommended updates via Dell SupportAssist and Windows Update. Everything installed successfully except for this specific KB. I have tried every standard troubleshooting step including manual installation of the update package from the Microsoft Update Catalog but with no success.
It seems there is a systemic conflict between the factory image on these new Dell units and this particular Windows 11 update, which also prevents DISM and ISO repairs from recognizing the systems as 'eligible'
Lara_M
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7 Posts
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March 19th, 2026 18:33
@BeastGamer13
Hello!
I have tried today installing offline. No positive result.
Lara_M
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March 19th, 2026 18:37
@Rohan furqan
Hello!
DELL-Nat M
Community Manager
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3.6K Posts
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March 23rd, 2026 14:38
Hi everyone,
To help us investigate and escalate this issue, could you please share the following details?
Once we have this information, we can proceed with further analysis and escalation.
CarloMax
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2 Posts
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March 23rd, 2026 15:38
Questo lo screenshot dell'errore. Succede su:
- Dell Pro Max T2
- Dell Tower ECT 1250
Entrambi nuovi e con Windows 11 Pro. Come già detto tutti gli aggiornamenti di Support Assist effettuati.
Per il momento ho sospeso gli aggiornamenti per 4 settimane in attesa di soluzione.
Lara_M
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7 Posts
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March 23rd, 2026 16:44
@DELL-Nat M
Thank you for being willing to help me/us.
My laptop is Dell Pro Max 16 MC16250 (purchased at the end of July 2025).
Windows 11 version 25H2 (OS Build 26200.7840) - I am not an Insider.
When I try to install KB5079473, I always get the same error: 0x800f0831.
DISM /Online /Cleanup-Image /RestoreHealth - result:
Error: 0x800f0915. "The repair content could not be found anywhere."
Mention: I had a remote session with Dell Assistance on the 14th of March.
For the moment I have stopped the updates.