If your Windows 11 backup stopped working in April 2026, you are not alone — and the culprit is almost certainly Windows security update KB5083769. Released on April 14, 2026 as part of Microsoft’s monthly Patch Tuesday rollout, this update has caused backup failures across a wide range of popular third-party backup tools. The good news is that Microsoft has acknowledged the issue and the fix is straightforward.

In this post, we explain exactly what is happening, which backup tools are affected, how to check whether your system is impacted, and what you need to do to get your backups running again — without uninstalling the update or leaving your PC exposed to security risks.

What Is Windows 11 Update KB5083769?

KB5083769 is the April 2026 cumulative security update for Windows 11, bringing Build 26200.8246 / 26100.8246 to affected devices. Like all monthly security updates, it patches known vulnerabilities, improves system stability, and tightens Windows’ overall security posture. This particular update also introduced a notable change: it added a new set of known vulnerable kernel drivers to the Windows driver blocklist.

The driver blocklist is a built-in Windows security feature that prevents drivers with known security weaknesses from loading on the system. This is a legitimate and important security measure — vulnerable drivers can be exploited by malware to gain elevated kernel-level access to a PC. By blocking them proactively, Microsoft reduces the attack surface for a whole class of exploits.

However, the side effect is that some third-party backup tools rely on drivers that are now on this blocklist — and when those drivers are blocked, backups fail.

Why Is KB5083769 Causing Backup Failures?

The update specifically introduces a new behavior involving the psmounterex.sys driver, which is used by various backup solutions to mount and manage storage images during the backup process. When Windows blocks this driver from loading — because it has been identified as a known vulnerable kernel driver — backup operations that depend on it can no longer complete successfully.

Affected users typically see one or more of the following error messages when attempting to run a backup:

• “The backup has failed because Microsoft VSS has timed out during the snapshot creation”
• “VSS_E_BAD_STATE”
• General “backup failed” notifications with no clear explanation in the backup software’s interface

VSS stands for Volume Shadow Copy Service — a core Windows component that backup tools use to create consistent point-in-time snapshots of your data. When the underlying driver is blocked, VSS cannot complete the snapshot, and the backup fails.

Importantly, Microsoft has confirmed this is not a bug in KB5083769. The driver blocking is working exactly as intended from a security standpoint. The issue is that some backup software vendors have not yet updated their drivers to use versions that are not on the blocklist.

Which Backup Tools Are Affected?

This is not an issue isolated to one or two backup products — it affects a broad range of popular solutions used by home users, IT professionals, and businesses. Confirmed affected tools include:

• Macrium Reflect
• Acronis Cyber Protect Cloud
• UrBackup Server
• NinjaOne Backup

The issue also extends beyond Windows 11. Users running Windows 10 and various versions of Windows Server have also reported backup failures after the April 2026 update, as the driver blocklist update was applied across multiple Windows versions.

How to Check If Your System Is Affected

If your backups are failing and you suspect KB5083769 is the cause, you can confirm it by checking the Windows Event Viewer for a specific driver-blocking event. Here is how to do it:

1. Press Windows + S, type Event Viewer, and open the application.
2. In the left panel, navigate to: Applications and Services Logs → Microsoft → Windows → CodeIntegrity → Operational
3. In the event list, look for entries with Event ID 3077 and the Policy ID {D2BDA982-CCF6-4344-AC5B-0B44427B6816}.
4. If you find entries matching this ID, your system has blocked a driver that falls under this new vulnerable driver policy — confirming the April update is causing your backup failures.

The presence of these Event ID 3077 entries is the clearest confirmation that the blocked driver is the root cause of your backup problem.

Microsoft’s Official Fix: Update Your Backup Software

Microsoft’s recommended resolution is simple: update your backup software to the latest available version. Backup vendors are now releasing updated versions of their tools that use newer, non-blocked driver versions that are compatible with the April 2026 security update.

Here is what to do:

1. Open your backup application and navigate to its update or help section.
2. Check for available updates and install the latest version of the software.
3. Once updated, run a test backup to confirm the issue is resolved.
4. If an update for your specific backup tool is not yet available, check the vendor’s support pages or community forums for a timeline or temporary workaround.

Microsoft is not recommending that users uninstall KB5083769 or pause Windows Update to work around this issue. Doing so would leave your system exposed to the security vulnerabilities that the April update was designed to address. The correct path is to keep your OS updated and update your backup software in parallel.

Should You Still Install KB5083769?

Yes — security updates should not be skipped, and KB5083769 is no exception. The driver blocklist changes it introduces close real security gaps. Vulnerable drivers are a known attack vector used by ransomware and rootkits to gain kernel-level access to systems. Blocking them proactively is a sound security practice.

If you haven’t yet installed the April update and you rely on third-party backup software, the smart approach is to:

1. Update your backup software first — check for the latest available version before applying the Windows update.
2. Install KB5083769 through Windows Update (Settings → Windows Update → Check for updates).
3. Run a test backup immediately after to confirm everything is still working.

If you are already running the April update and experiencing backup failures, the same advice applies — update your backup software and test. The OS update itself does not need to be reversed.

Keep Your Windows License Up to Date

Issues like KB5083769 are a reminder of just how important it is to stay current with Windows security updates. Staying on an outdated or unactivated version of Windows means missing critical security patches that protect your system from driver exploits, ransomware, and other threats.

If you’re running an unactivated copy of Windows or still on an older version, now is a great time to upgrade. Wincdkey offers genuine, lifetime Windows 11 keys at the lowest available price — including:

• Windows 11 Pro — the best choice for professionals and business users who need BitLocker, Remote Desktop, and advanced security features
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• Windows 11 Enterprise — for large organisations needing advanced threat protection and centralised management

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Still on Windows 10? Microsoft’s end-of-support deadline for Windows 10 is October 14, 2025 — and security updates like KB5083769 confirm just how critical staying on a supported OS version really is. If your hardware supports it, upgrading to Windows 11 is the right move. Browse our full range of Windows licenses to find the edition that fits your needs.

Summary: What You Need to Do

• ✅ Don’t uninstall KB5083769 — it is a legitimate and important security update
• ✅ Update your backup software to the latest available version from your vendor
• ✅ Check Event Viewer for Event ID 3077 to confirm whether a driver is being blocked on your system
• ✅ Run a test backup after updating your backup software to confirm the issue is resolved
• ✅ Stay on a genuine, activated Windows license to ensure you always receive security updates — browse our Windows 11 keys at Wincdkey

Have questions about Windows activation or need help choosing the right Windows license? Our team is available 24/7 via the Help & Support Center, and you can find answers to common questions in our FAQs.