Fix 0xC01C0003: Async Requests Not Valid for This Operation

Cause 1: A Misbehaving Minifilter Driver (Most Common)

This error shows up when a minifilter driver—like those used by antivirus software, backup tools, or disk encryption—sends an async request that Windows' filter manager can't handle. I've seen this for years on Windows 10 build 1909 and Windows 11 22H2. You'll usually get the error when opening a file or running a backup job.

The quickest fix? Check which filter drivers are loaded and remove the troublemaker.

How to Find the Bad Driver

1. Open Command Prompt as administrator. Press Win + X, then select "Terminal (Admin)" or "Command Prompt (Admin)".
2. Type fltmc instances and press Enter. This lists all filter drivers and their status.
3. Look for any driver with an "Altitude" value that seems odd—like a third-party driver (not Microsoft) sitting very low (below 100000) or very high (above 400000). Common offenders: Symantec, McAfee, Carbonite, Veeam.

If you see a driver you don't recognize, note its name. Then run:

fltmc unload <drivername>

Replace <drivername> with the name (like SymcFilter). This unloads it temporarily. Test if the error goes away. If it does, uninstall the associated software completely.

If You Can't Unload It

Some drivers won't unload because they're in use. Reboot into Safe Mode—press F8 at startup or use Shift + Restart from the sign-in screen. Then run fltmc unload again. If it still refuses, you'll need to uninstall the software from Control Panel.

Cause 2: Corrupted Filter Manager Cache

Sometimes the filter manager itself gets confused. This happens after a failed update or a sudden power loss. The error might appear in random apps, not just one program.

Here's the fix I've used a dozen times on Windows 10 and 11:

1. Open an elevated Command Prompt or PowerShell.
2. Run sfc /scannow—this checks system files. Let it finish. It'll fix any corrupted system files.
3. Then run DISM /Online /Cleanup-Image /RestoreHealth. This fixes the component store. It takes a few minutes.
4. Reboot your PC.

I've seen this clear the error for users who had no third-party filter drivers at all. The system file checker (sfc) replaces corrupted filter manager files. DISM makes sure the whole system image is clean.

Cause 3: Buggy Third-Party Software That Registers Its Own Filter

Some apps install their own minifilter driver even when you don't expect it. Cloud sync tools like Dropbox (version 150 and older), Google Drive for Desktop, and even some printer management software do this. The error pops up when you save a file through that specific app.

To find these hidden filters:

1. Run fltmc filters in an admin command prompt. This shows the filter name, altitude, and the number of instances.
2. Look for filters that aren't from Microsoft. They usually have odd names like ProcessMonitor, FileSyncFilter, or EPSFilter.
3. Check the altitude value. Microsoft's built-in filters have altitudes between 200000 and 400000. Third-party ones often sit outside that range.

Once you identify the suspect, you have two choices:

• Update the software—visit the vendor's site and grab the latest version. Many bugs were already fixed.
• Disable the filter—if updating doesn't help, uninstall the software completely. Reinstall it later after they release a patch.

One trick: you can disable a filter without uninstalling the app by renaming its driver file. For example, for Dropbox, go to C:\ProgramData\Dropbox\Update\ and rename DropboxFilter.sys to DropboxFilter.old. Reboot. But this might break the software—only do it as a temporary test.

Quick-Reference Summary Table

I know this error is annoying—especially when it stops you from working. Start with the first cause. Nine times out of ten, it's a driver from an overzealous antivirus or backup tool. If that doesn't work, the SFC/DISM route has saved me more than once. Good luck!