Windows failed update 25H2, error code 0xc1900101

Question

Windows failed update 25H2, error code 0xc1900101

Francesco Santoro 0

I saw this problem is usually related to drivers and Ihave removed some outdated drivers but nothing changed. I saw a solved answer with this same error code but it seemed to be specifically tailored for that other user and his specific driver issues.

I also tried updating it while disconneting any other device except my screen to no avail.

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2 answers

Your answer

Answer 1

Ramesh Srinivasan 86,840 Independent Advisor

Hi Francesco,

You're right. 0xC1900101 is usually caused by outdated device drivers or BIOS. Please do the following:

Step 1:

To analyze the issue and check the extended error code, please upload the following setup log files to OneDrive or GoFile.io and post the link here:

C:\$WINDOWS.~BT\Sources\Panther\setupact.log

C:\$WINDOWS.~BT\Sources\Rollback\setupact.log

Note: C:\$WINDOWS.~BT is a hidden folder. To access it, press Win + R, type C:\$WINDOWS.~BT and click OK.

Add the files to a zip archive and upload it.

Step 2:

Enable Memory Integrity. To do so, go to Windows Security → Device security → Core isolation details → Memory integrity. If the page lists any incompatible drivers, please post a screenshot.

Francesco Santoro 0 Reputation points

2026-09-09T12:56:29.5+00:00

Alright, here should be everything, it does schow incompatible drivers in the core isolation page: https://gofile.io/d/mi8J3rKv
Ramesh Srinivasan 86,840 Reputation points Independent Advisor

2026-09-09T14:03:58.92+00:00
The following driver is incompatible with Memory Integrity.

(NEPKernel)- Driver Path: V:\SteamLibrary\steamapps\common\Farlight 84\WindowsClient\Solarland\Binaries\Win64\NEPKernel.sys

Can you please uninstall Farlight 84, restart Windows, and try to enable Memory Integrity?
Francesco Santoro 0 Reputation points

2026-09-09T15:02:50.59+00:00

I have enabled memory integrity and restarted my PC. Should I try reinstalling the update at this point?
Ramesh Srinivasan 86,840 Reputation points Independent Advisor

2026-09-09T15:04:48.08+00:00

Yes. Please try the in-place upgrade now.

(If the setup still fails, share the latest setup logs. We may have to remove additional drivers using a specialized tool called FRST.)
Francesco Santoro 0 Reputation points

2026-09-10T09:10:47.11+00:00

I have gotten the same install error after retrying, here are the newer logs: https://gofile.io/d/Huks7HgD
Ramesh Srinivasan 86,840 Reputation points Independent Advisor

2026-09-10T09:12:18.9833333+00:00

The files in that link are inaccessible. I get the following error:

This content is not publicly accessible

To make this content publicly accessible, its owner must change its visibility settings.
Francesco Santoro 0 Reputation points

2026-09-10T09:15:36.53+00:00

Sorry I thought I fixed it, must've missclicked, https://gofile.io/d/Huks7HgD
Ramesh Srinivasan 86,840 Reputation points Independent Advisor

2026-09-10T09:17:47.3066667+00:00
Please share your Farbar scan logs for analysis.

Download Farbar Recovery Scan Tool 64-bit FRST64.exe

If the OS language is not English, rename FRST64.exe to FRST64English.exe.

Run the program. Don't check or uncheck any options. Click "Scan".

Add the two logs, FRST.txt and Addition.txt, to a zip archive.

Share the zip file on OneDrive or GoFile.io, and post the link here.

Note: If Microsoft Edge or Chrome mislabels the Farbar Scanner executable as PUA/malware, choose to keep it by tapping … in the bottom bar, choosing Keep, and then choosing Keep anyway in the dialog that appears. See this screenshot. It's a safe tool used in most antimalware forums.

Standard Disclaimer: There is a link to a non-Microsoft website. The page appears to provide accurate, safe information. Watch out for ads on the site that may advertise products frequently classified as PUPs (Potentially Unwanted Products). Thoroughly research any product advertised on the site before you decide to download and install it.
Francesco Santoro 0 Reputation points

2026-09-10T10:00:23.5366667+00:00

Here it is: https://gofile.io/d/kJJpHUfm
Ramesh Srinivasan 86,840 Reputation points Independent Advisor

2026-09-10T10:04:30.2833333+00:00

Please backup the registry using Acelogix Regbak.

Let me know once it's done.

Standard Disclaimer: There is a link to a non-Microsoft website. The page appears to provide accurate, safe information. Watch out for ads on the site that may advertise products frequently classified as PUPs (Potentially Unwanted Products). Thoroughly research any product advertised on the site before you decide to download and install it.
Ramesh Srinivasan 86,840 Reputation points Independent Advisor

2026-09-10T10:07:44.87+00:00

Note: Before doing so, please uninstall Malwarebytes Antimalware completely. Reboot Windows and backup the registry using RegBak.
Francesco Santoro 0 Reputation points

2026-09-10T11:34:57.93+00:00

Ok I have created a backup, what now?
Ramesh Srinivasan 86,840 Reputation points Independent Advisor

2026-09-10T11:42:07.5866667+00:00

Have you uninstalled Malwarebytes?
Francesco Santoro 0 Reputation points

2026-09-10T11:44:54.4133333+00:00

Yes, I have uninstalled Malwarebytes, rebooted my PC, then used RegBak to create a backup of the registry
Ramesh Srinivasan 86,840 Reputation points Independent Advisor

2026-09-10T11:46:33.72+00:00
Please run the fixlist below to remove some 3rd party drivers and clean up the driverstore.

Download fixlist.txt

Save Fixlist.txt to the same folder as FRST64English.exe.

Close all programs.

Launch the Farbar Scanner tool and click "Fix".

Restart Windows if prompted.

Upload the output log file (FixLog.txt) in your next reply.

NOTE: The fixlist.txt script was written specifically for this user and for use on that particular machine. It is not recommended to run it on another machine, and don't run the same fixlist.txt more than once.
Francesco Santoro 0 Reputation points

2026-09-10T11:49:01.1566667+00:00

Ok, I will do that, just a quick question beforehand. I understand I made a backup because modifying the registry can cause problems, but how exacctly can I use the backup in case windows fails to booth?
Ramesh Srinivasan 86,840 Reputation points Independent Advisor

2026-09-10T11:50:52.57+00:00

All those hives are saved to C:\Windows\Regbak. They can be restored via Windows RE.

Also, the fixlist.txt creates a System Restore point.
Francesco Santoro 0 Reputation points

2026-09-10T12:04:34.4733333+00:00

Ok, all done, here is the fixlog: https://gofile.io/d/UfO8cSuQ
Ramesh Srinivasan 86,840 Reputation points Independent Advisor

2026-09-10T12:07:07.9866667+00:00

It ran correctly. Please clean-boot Windows using msconfig.exe (Reference: How to perform a clean boot in Windows | Microsoft Support)

Re-run the 25H2 setup and let me know how it goes.

Answer 2

0xC1900101 usually means the update is failing because of an incompatible or unstable driver. Since external devices were already disconnected and some old drivers were already removed, the next useful checks are the built-in driver and system repair steps.

Check Device Manager for driver errors
- Open Start and type Device Manager.
- Look for any device with a yellow exclamation mark.
- Right-click that device and choose Update Driver Software or Uninstall.
- This helps identify drivers that are still blocking the upgrade.
Install all available Windows Update items
- Run Windows Update multiple times.
- Install all available software updates, hardware updates, and third-party driver updates.
- If Windows Update has problems, run the Windows Update troubleshooter:
  - Start > Settings > System > Troubleshoot > Other troubleshooters > Windows Update > Run
Update third-party drivers from the hardware manufacturer
- Check the manufacturer sites for recently added hardware, especially graphics, network, and storage-related drivers.
- 0xC1900101 is commonly tied to outdated or incompatible drivers.
Remove third-party security software temporarily
- Uninstall non-Microsoft antivirus or security software before retrying the upgrade.
- Make sure the installer or product key information is available first.
- Windows Defender can protect the device in the meantime.
Do a clean boot, then retry the upgrade
- A clean boot starts Windows with a minimal set of drivers and startup programs.
- This is recommended for rollbacks caused by driver conflicts.
- Use the Microsoft clean boot procedure, then start the 25H2 upgrade again.
Repair disk and system files
- Open Command Prompt as administrator.
- Run:
  - chkdsk /f C:
  - DISM.exe /Online /Cleanup-image /Restorehealth
- chkdsk may require a restart. These steps can fix file system and Windows image issues that interfere with setup.
Confirm free space
- Make sure there is at least:
  - 16 GB free for 32-bit Windows
  - 20 GB free for 64-bit Windows
If the failure continues, review setup logs
- For 0xC1900101, useful logs include:
  - $Windows.~bt\Sources\Rollback\setupmem.dmp
  - $Windows.~bt\Sources\Rollback\*.evtx
  - $Windows.~bt\Sources\Rollback\setupapi\setupapi.dev.log
- For some 0xC1900101 cases, also check:
  - %windir%\Panther\Setuperr.log
  - %windir%\Panther\Setupact.log
- These logs can reveal the exact driver causing the rollback.

If the update is specifically failing during a later boot phase, Microsoft’s guidance for 0xC1900101 also points to display, storage, antivirus, BIOS, or other incompatible drivers as common causes.