Solved KB5021255 install issue

KB5021255 issue. The update downloads and proceeds to install, but when nearing 99%, I get the following message : “Something didn’t go as planned. No need to worry – Undoing changes. Please keep your computer on”. The computer does indeed go back to its initial state, and then reloads the update. I’ve done the usual stuff – dism, sfc scannow..., everything flags up as ok - and then tried again, to no avail. I’ve put the updates on pause for now. Any (kind) suggestions to try?

little jim said:

KB5021255 issue. The update downloads and proceeds to install, but when nearing 99%, I get the following message : “Something didn’t go as planned. No need to worry – Undoing changes. Please keep your computer on”. The computer does indeed go back to its initial state, and then reloads the update. I’ve done the usual stuff – dism, sfc scannow..., everything flags up as ok - and then tried again, to no avail. I’ve put the updates on pause for now. Any (kind) suggestions to try?

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I have found, that when an update fails to install and the system rolls back, most often the next update will install. Since updates are cumulative, the newer update will have the failed update improvements included. I have never been able to establish what caused the failure or how to prevent it from happening. If updates continue to fail, you may need to try more advanced solutions.

Hello and welcome to the forum. Run these procedures, then try again..

1. Disable all third party antivirus software, including Malwarebytes. Use task manager to make sure all their processes are not running.

1. run troubleshooter-settings>system>troubleshoot>other troubleshooters>windows update-RUN.

2. Reset Windows update using Brink's tutorial Reset Windows Update in Windows 11 Tutorial

3. Run system file checker. Open command prompt as administrator and type sfc /scannow. If SFC finds anything it can not repair perform DISM as in step 4. If SFC finds and corrects all errors, try windows update again. If Windows will still not update, perform step 5

4. run dism /online /cleanup-image /restorehealth from an administrative command prompt. Then restart and follow-up with another sfc /scannow to see if dism fixed anything.

5. Do a repair install. Repair Install Windows 11 with an In-place Upgrade Tutorial

With Windows 11 22H2 I had significant problems installing monthly update rollups like these. In my case, I solved it by uninstalling Malwarebytes Antivirus + ZoneAlarm firewall and moving to ESET internet security instead.

Thanks for all the suggestions, will try today and give feedback.

Tried, with no success :
- Removing bitdefender antivirus,
- Troubleshooter
- Resetting windows update,
- Double checking with dism (all) and sfc (all was good)

Did not do a repair install of win11, the option to keep apps was greyed out.
For my education, is there a difference between doing repair install and doing dism...restore health followed by sfc /scannow ?

Soooo... reintalled bitdefender, to have an antivirus that updates, and postponed windows updates. I'll follow Sir George's above words of wisdom and be patient, unless something obvious turns up. Thanks to all.

little jim said:

For my education, is there a difference between doing repair install and doing dism...restore health followed by sfc /scannow ?

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Repair Install = REPLACE ALL WINDOWS 11 FILES and, optionally, save all your data & apps, at the the build level of the .iso you use
- you may need to run 'Windows Update' to get you back to your previous build level

Dism + Sfc = TRY TO REPAIR WINDOWS 11 FILES IN-SITU - will not necessarily work

Given IanMosely's bold (forgive the pun) statement above, I tried once again to do a repair-install, as initially suggested by glasskuter.

My previous attempt - with win11 downloaded directly to a usb drive via the media creation tool - had the "keep apps" greyed out. This time I downloaded the disk image ISO and made a bootable usb drive with rufus (v3.21).

Lo and behold, the "keep apps" option was now available. Followed the tuto, and SUCCESS!
In fact, the troublesome kb5021255 update disappeared after the repair-install, so presumably has been integrated into the latest ISO.

Once again, thanks to all.

Glad to hear you fixed it. Sorry you spent the time on the other steps, only to have the last thing on the list fix it, but the end result is what is important. That list is basically things to try in order of severity when chasing a WU problem and has worked for a lot of people who have problems with the cumulatives. It hasn't worked for everyone though as there is no rhyme or reason why some experience the issue and some don't.

Epilogue : 24h after the successful repair-install, the kb5021255 update reappeared. This time the update went smoothly.

I am also the victim of the KB5021255 issue. On December patch Tuesday I got 3 Windows 11 updates. Two of them installed fine (with anti-virus active and all). The third one - KB5021255 failed at 97% completion with the same error message = “Something didn’t go as planned. No need to worry – Undoing changes. Please keep your computer on”.

I have tried all of the current and previous noted Windows updates solutions including -
- Troubleshooter (no issues)
- Resetting Windows update (multiple times)
- Double checking with dism (all good) and sfc (all good)
- Running stand alone .msu update for KB5021255
- Running stand alone .cab update for KB5021255

And all still failing at the 97% installation progress point for KB5021255.

I find it completely ridiculous that a software company that has been in business for over 30 years still cannot get Windows updates properly tested before they push them out. It is very annoying that the end users have to become the QA testers and resort to jumping through various hoops such as having to uninstall / reinstall anti-virus (when all other updates work fine with antivirus functional), or to have to download the entire O/S .iso file and to a repair install - all for just a Windows update.

Hopefully, Microsoft is seeing all of the various forums with this problem for KB5021255 and that they issue a properly working update in January's patch Tuesday. I have just paused all Microsoft updates for several weeks and will try again after next patch Tuesday, unless someone believes that there is an actual working solution to this issue for KB5021255