What happened
Microsoft has confirmed and fixed a bug introduced by this month's Windows security updates that broke File History, the built-in backup tool many home users and small businesses rely on to protect their Documents, Pictures, Videos, Music and Desktop folders.
After installing the September 2026 security update, affected systems started showing "Reconnect your drive" prompts even when a compatible backup drive was properly connected, along with "No previous version available" messages and backup timestamps that stopped updating. Behind the scenes, File History was crashing, with Event Viewer logging failures tied to FileHistory.exe and KERNELBASE.dll.
The issue hit devices running Windows 10 version 21H2 and later, Windows 10 Enterprise LTSC 2016/2019, and Windows 11 version 23H2 and later — a wide slice of the currently supported Windows fleet.
Why it matters
File History (and its successor, Windows Backup) is the last line of defense against accidental deletion, ransomware, or drive failure for many home users and small offices that don't run dedicated backup software. A backup tool that silently stops working — while still reporting the drive as connected — is arguably worse than one that's obviously broken, because people may believe they're protected when they aren't.
It's also the latest in a run of stability problems tied to September's Patch Tuesday, which separately triggered Hyper-V failures, Remote Desktop Services outages, USB audio issues, and a domain-login bug — all needing follow-up fixes inside the same two-week window.
What to do
- Windows 11 users: install this month's optional cumulative update — KB5124006 (Windows 11 26H1) or KB5124010 (Windows 11 24H2/25H2) — to get the fix now.
- Skipping optional updates? The fix rolls into the mandatory October 13 Patch Tuesday release.
- Windows 10 users: no dedicated fix has been detailed yet; watch official Microsoft update channels for your build.
- Whatever your platform, confirm your backups are actually current — check the "Last Backup" timestamp under Control Panel > System and Security > File History, and don't rely on File History alone for critical data until you've verified it's working.