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KB5066791 cannot be installed, Error code: 0x80070643.
Hello everyone, I've had problems updating for a while now and I found another post where someone had a similar problem (https://learn.microsoft.com/de-de/answers/questions/5768523/kb5066791-kann-nicht-installiert-werden-fehlercode). The problem is that I have no idea how to check if my error is due to the same reasons. If someone wants to help me, I can provide the CBS.log file.
Thank you for taking the time to read this
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Warum um Gottes Willen stellst du die Frage auf Englisch, obwohl im deutschsprachigen Forum und über dein deutschsprachigen Windows?
Warum liest du das Thema, das du verlinkt hast, selbst nicht zum Ende?
Der letzte Beitrag von Alvise Cervellati vom 12. Feb. 2026, 08:25 ist vom Fragesteller als hilfreich auskommentiert.
Vielen Dank für den Hinweis, hatte nicht drauf geachtet dass ich auf dem deutschsprachigen Forum bin. Außerdem hatte ich einen etwas anderen Fehlercode als in dem verlinkten Post und ich will generell eher vorsichtiger sein wenn es um das löschen/reinstallieren von wichtigen Dateien geht.
Hi. I'm David, and I'm happy to help you.
Please share the log file "CBS.log".
This file is stored in the directory: C:\Windows\Logs\CBS
Copy the file to your desktop or another easily accessible folder and store it in a ZIP file. Then, upload the ZIP file to the cloud (OneDrive) and choose it to get the link.
Post the link to the ZIP file here so I can have a look.
Looking forward to your reply.
Thanks for responding, here is the link to the log file https://1drv.ms/u/c/de86a2989757bb8b/IQDf8lUUAaRiTIMcXIl7_WOWAd_UR8JkzBNbLoDQI2X84xE?e=cLN5j
Sorry for the delay in reply. I've been offline.
Thanks.
The log shows that the Windows Update agent initiates planning for the KB5066791 update packages. However, there are no explicit critical access violation failures or corrupted files specifically recorded in this section of the CBS log for this package.
Error code 0x80070643 is a generic error meaning ERROR_INSTALL_FAILURE. When it occurs in Windows 10 cumulative updates, it is usually related to failures in the .NET Framework ecosystem, space issues on critical partitions, or conflicts with antivirus/background repair tools.
Before proceeding with the recommended steps, could you clarify if you have any third-party antivirus software installed? If so, which one?
Looking forward to your reply.
As far as I know I have no third party antivirus software installed. I have tried to use repairt tools recently so I would assume its connected to that.
Thanks for the clarification.
Which repair tools are you referring to? And where did you download them from?
Looking forward to your reply.
Maybe repair tool is the wrong word I used the Windows update troubleshooter.
Thanks for the clarification.
In this case, I suggest doing the following:
Rename the software distribution folders as instructed below:
cmd, right-click on "Command Prompt", and select "Run as administrator".net stop bits
net stop wuauserv
net stop cryptsvc
ren %systemroot%\softwaredistribution softwaredistribution.bak
ren %systemroot%\system32\catroot2 catroot2.bak
net start bits
net start wuauserv
net start cryptsvc
If it persists, use the system file checker to repair possible corrupted or missing system files.
cmd, right-click on "Command Prompt", and select "Run as administrator".dism.exe /online /cleanup-image /scanhealth
dism.exe /online /cleanup-image /restorehealth
dism.exe /online /cleanup-image /startcomponentcleanup
sfc /scannow
Note: Pay close attention to the results of the commands. This will help you determine whether the procedure was completed successfully or if there was a problem. If you get any errors, let me know the error message that was displayed.
If it persists, download and install the update that is having problems manually.
Download the installation package from the link below.
Source: https://www.catalog.update.microsoft.com/Search.aspx?q=KB5066791
If the problem persists, please let me know, and I will provide another method.
Feel free to ask any questions you may have.