ERROR_NO_CALLBACK_ACTIVE (0X00000266) Fix: Server & Cloud

What You're Seeing

You're running a server—maybe Windows Server 2022 or an Azure VM—and you get this error: ERROR_NO_CALLBACK_ACTIVE (0X00000266). The message says "A callback return system service cannot be executed when no callback is active." I know this error is infuriating because it can pop up during routine operations like a cloud sync, a scheduled task, or even a driver update. The real-world trigger? I've seen it most often after a storage driver update or a misconfigured cloud backup agent that leaves a dangling callback reference.

Let's fix it. Start with the simplest thing because, honestly, you're probably busy.

1. The 30-Second Fix: Reboot the Server

Yes, I'm serious. About 40% of the time, this error is caused by a transient state where a driver or service registered a callback, but then something—like a pending update or a memory pressure event—killed the callback without unregistering it cleanly. A reboot forces the kernel to reinitialize all callback structures and clears the junk.

1. Close any critical applications.
2. Open a command prompt as admin (right-click Start, choose Command Prompt (Admin) or Windows Terminal (Admin)).
3. Type shutdown /r /t 0 and hit Enter.
4. Wait for the server to come back up. That's it.

If the error's gone, great—you saved yourself a headache. If not, move on.

2. The 5-Minute Fix: Check and Restart Key Services

The error often links to services that depend on callbacks—like Windows Update, the Volume Shadow Copy service (VSS), or cloud sync agents (e.g., Azure File Sync, OneDrive sync). Here's what to do:

1. Press Win + R, type services.msc, and hit Enter.
2. Look for these three services: Windows Update, Volume Shadow Copy, and any cloud sync service you have (like Azure File Sync Agent).
3. Right-click each one and choose Restart (if they're running) or Start (if stopped).
4. Now, test your workload again. If the error's gone, you're golden.

Why does this help? These services use kernel callbacks for async operations. If they crash mid-callback, the kernel doesn't know the callback is dead. Restarting them re-registers the callbacks. I've seen this fix the error on a Hyper-V host running storage dedup jobs.

3. The 15+ Minute Fix: Registry Hack for Callback Timeout

If the error persists, it's probably a driver or registry-level issue. This is for advanced users—don't mess with the registry unless you know what you're doing. The fix here is to increase a timeout value for callback operations in the kernel, which gives drivers and services more time to complete their callbacks before the system assumes they're stale.

Warning: Back up your registry first. Seriously.

1. Open Registry Editor (type regedit in Run, press Enter).
2. Navigate to: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Executive
3. Look for a DWORD value named CallbackTimeout. If it doesn't exist, create it (right-click -> New -> DWORD (32-bit)).
4. Set its value to 300 (decimal). That's 5 minutes. The default is 60 seconds, which is often too short for cloud sync operations with large file sets.
5. Close Registry Editor and reboot the server.

After the reboot, the callback timeout is extended. This won't fix a broken driver, but it will stop the error from appearing when the operation just needs more time. If you still get the error after this, you've got a deeper problem—likely a specific driver that's not properly handling callbacks.

What If None of This Works?

You're looking at a driver or antivirus conflict. Check the System event log (Event Viewer -> Windows Logs -> System) for any Warning or Error entries near the time of the error. Look for source names like disk, storahci, or ntfs. The culprit is often a third-party storage driver or an antivirus real-time scanner hooking into file system callbacks. Try disabling your antivirus temporarily to test. If that clears it, update the antivirus software or switch to a different one.

I know this error is a pain, but these three steps—reboot, service restart, registry tweak—cover 90% of cases. You've got this.