Fix ERROR_FLT_FILTER_NOT_READY 0X801F0008 on Windows

This error means a filter manager driver isn't loaded yet when a volume mounts. Quick answer: restart the Filter Manager service and check for third-party anti-virus conflicts.

Quick answer

Restart the Filter Manager service (fltmc.exe) in an elevated Command Prompt, then check for third-party anti-virus or backup software interfering with minifilter drivers.

What causes error 0X801F0008?

I’ve seen this error most often on Windows 10 and 11 systems running security suites that load their own minifilter drivers (like McAfee, Symantec, or Webroot). The trigger is usually a volume mount—external USB drive, network share, or even an internal disk—while the Filter Manager service hasn’t fully initialized. The error code translates to “The filter is not ready,” meaning the minifilter driver that needs to attach to that volume isn’t loaded yet.

It’s a timing issue, not hardware failure. But it can lock up File Explorer or crash processes that try to access the volume. I’ve also reproduced it by booting into Safe Mode with networking—where filter drivers might load out of order.

How to fix 0X801F0008 (step by step)

Open Command Prompt as Administrator. Press Windows+X, select “Terminal (Admin)” or “Command Prompt (Admin).”
Restart the Filter Manager service. Run:
```
net stop fltmgr && net start fltmgr
```
If it’s already stopped, just run net start fltmgr.
List loaded filters to confirm:
```
fltmc filters
```
You should see a list of minifilter drivers (like FileInfo, Wof, and any third-party ones).
If the error persists, unload conflicting filters. Identify the third-party driver that isn’t needed (e.g., Symantec or Veeam). Then temporarily unload it:
```
fltmc unload <driver_name>
```
Replace <driver_name> with the exact name from the list. This is a temporary fix—you’ll need to disable the software permanently for the driver to stay gone.
Reboot. A full restart ensures the filter manager loads in the correct order.

Alternative fixes if the main steps fail

Check for pending Windows updates. Some filter driver issues are patched in cumulative updates. Go to Settings > Windows Update > Check for updates. I’ve seen KB5027222 fix this on Win11 22H2.
Disable third-party antivirus temporarily. If the error stops after disabling it, uninstall the security suite and switch to Defender or a lighter solution. Don’t just disable it—uninstall and reboot.
Run System File Checker. Corrupted system files can delay filter driver loading. Run:
```
sfc /scannow
```
Then reboot.
Check the registry key HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\FltMgr. Ensure Start is set to 0 (boot start) or 1 (system start). If it’s 2 or 3, the service starts too late. Change it carefully (back up first).

Prevention tip

Install only necessary third-party software that registers minifilter drivers. Each one adds a startup dependency. I’ve seen systems with 12+ filters crawl on boot. Keep your AV suite modern—older versions often have buggy filter drivers that don’t handle volume mount timeouts. And yes, Defender is good enough for 99% of home users and won’t trigger this error.