Windows 11 File History Not Working After KB5124008: Cause and Fix

Did your PC start saying “Reconnect your drive” even though your backup drive is plugged in and working? Or does File History show a “Last backup” date from weeks ago? You did not break anything. A Windows update did.

The September 2026 update, KB5124008, caused a bug that stops File History from making or updating backups on some PCs. The worst part is that it fails quietly, so many people do not notice until they need a file back. Here is how to check if you are affected, how to fix it, and how to protect your files in the meantime.

Quick Answer

• The bug came with KB5124008, the September 8, 2026 update (builds 26200.9445 and 26100.9445)
• Your backup drive is fine. Microsoft confirmed this is a Windows bug
• The official fix is in the optional update KB5124010. Install it from Settings > Windows Update > Advanced options > Optional updates
• If you skip the optional update, the fix arrives with the October 13, 2026 Patch Tuesday update
• The emergency update KB5129195 did not fix this
• Some users still report leftover problems after installing the fix
• Until File History works again, copy your important files somewhere else

How to Check If You Are Affected

Open Control Panel > System and Security > File History and look for these signs:

1. A message saying “Reconnect your drive” even though the drive is connected and works normally in File Explorer
2. A “Last backup” time that is old, stuck, or clearly wrong
3. “No previous version available” when you try to restore a file you changed recently
4. In some cases, crash entries in Event Viewer (under Windows Logs > Application) that mention FileHistory.exe and KERNELBASE.dll

Then check your Windows build under Settings > System > About:

• 26200.9445 or 26100.9445 means you have KB5124008 without the fix
• 26200.9457 or 26100.9457 means you also have the emergency update KB5129195, which still does not fix File History
• 26200.9550 or 26100.9550 means you have KB5124010, which includes the fix

Why Did This Happen

Microsoft says that after installing KB5124008, some people using File History may be unable to create or update backups. It has not shared how many PCs are affected. In independent testing, the bug showed up on many setups, including a brand new drive that worked perfectly everywhere else.

The “Reconnect your drive” warning is false. The drive is not the problem. The bug is inside Windows.

Fix 1: Install the Optional Update KB5124010 (Best Option)

This is the fix Microsoft points to. It is an optional update, so Windows will not always install it on its own.

1. Go to Settings
2. Click Windows Update
3. Click Advanced options
4. Click Optional updates
5. Select KB5124010 and click Download and install
6. Restart your PC
7. Open File History and click Run now, then check that the “Last backup” time updates

If you do not see it, click Check for updates first. You can read what else is inside this update in our KB5124010 guide.

Fix 2: Wait for the October 13 Update

If you would rather not install optional updates, you do not have to. Microsoft says the fix will also come with the regular October 2026 Patch Tuesday update on October 13. The catch is that File History stays broken until then, so keep your files safe another way (see below).

One more date matters here. If you are on Windows 11 24H2 Home or Pro, updates end on October 13 too. Our Windows 11 versions guide explains how to move to 25H2 so you keep getting fixes.

Fix 3: Uninstall KB5124008 (Last Resort Only)

Some users on Microsoft’s forums say uninstalling the update brought File History back. But there is a real cost. KB5124008 also carries important security fixes, including for flaws that attackers were already using. Removing it leaves your PC exposed, so only try this if you cannot install KB5124010.

1. Go to Settings > Windows Update > Update history
2. Click Uninstall updates
3. Find KB5124008 and click Uninstall
4. Restart your PC
5. Pause updates so it does not install again straight away

Treat this as temporary, and install the fixed update as soon as you can.

Still Not Working After Installing KB5124010?

Some users report that backups work again after the fix, but a leftover problem remains. For example, clicking Run now does not update the last backup time, or restore still says “No previous version available”. So the fix may not be complete for everyone yet.

Restart your PC and try Run now once more. If the problem continues, do not rely on File History for now. Use one of the backup methods below until Microsoft’s next update.

Protect Your Files Right Now

Do this today, whichever fix you choose:

1. Copy your important folders by hand. Copy Documents, Pictures, Desktop, and anything you cannot lose to an external drive or USB stick. It takes a few minutes and works even when backup tools fail.
2. Turn on OneDrive folder backup. In the OneDrive settings, look for Sync and backup and Manage backup (menu names can vary a little). This gives you a cloud copy of your main folders.
3. Try a different backup tool. Free options such as FreeFileSync can copy folders to a drive on a schedule. Check any tool yourself before trusting it with important files.

How This Update Story Fits Together

For the full running list of updates, see our latest Windows 11 updates page. This is not the only update problem this year. In August, an update caused BIOS trouble on some laptops, which we covered in our KB5121003 guide.

Frequently Asked Questions