Fix ERROR_CS_ENCRYPTION_FILE_NOT_CSE (0X00001785)

Quick answer: This error fires when Windows Controlled Folder Access blocks an app from encrypting a file that isn't already marked as CSE (Controlled State Encryption). Turn off CFA for that app, or add the file's folder to CFA's protected list.

What's Actually Happening Here

I've seen this error pop up mostly in corporate environments where IT enforces Controlled Folder Access alongside BitLocker or third-party encryption tools like Dell Data Protection or McAfee File Encryption. The short version: Windows Defender thinks your app is ransomware trying to encrypt a file that wasn't authorized for encryption.

Windows 10 version 1709 and later (including Windows 11) introduced Controlled Folder Access as a ransomware shield. It monitors apps that try to modify files in protected folders. If the file hasn't been flagged with the CSE attribute—meaning it's not part of a controlled encryption state—Windows slams the door shut with error 0x00001785.

This tripped me up the first time too, back when I was setting up BitLocker on a Surface Pro 7. The app looked legit. Windows didn't care.

Fix Steps: Clear the Block

Identify the app triggering the error. Open Event Viewer (eventvwr.msc) > Windows Logs > System. Filter by Event ID 12 (or 11) from source Microsoft-Windows-Windows Defender. The log entry will name the blocked executable.
Add the app to CFA's allowlist. Go to Windows Security > Virus & threat protection > Manage ransomware protection > Allow an app through Controlled folder access. Hit Add an allowed app and browse to the blocked .exe. This works for most third-party encryption tools.
If the file is already encrypted, mark it as CSE. Open an admin PowerShell and run:
```
fsutil file setcse C:\path\to\file.txt
```
Replace the path with your actual file. This sets the encrypted attribute that Windows expects.
Restart the encryption process. Some tools (like 7-Zip AES encryption) will now run without the error. If you're using BitLocker or built-in EFS, a restart might be needed.

When the Main Fix Doesn't Work

Sometimes the app still refuses. Here's what I'd try next:

Disable Controlled Folder Access temporarily. Not ideal for security, but if you're in a hurry and the file is safe, flip the toggle off in Windows Security. Re-enable it after the encryption completes.
Move the file outside protected folders. CFA typically guards Documents, Desktop, Pictures, and Videos folders. Try encrypting the file from C:\Temp or another non-protected location.
Check for group policy conflicts. In corporate settings, IT might enforce CFA via GPO. Run gpresult /h gp.html and look for Controlled Folder Access policies. If locked, you'll need admin approval to whitelist the app.
Update the encryption tool. Older versions of VeraCrypt (before 1.24) and some EFS wrappers don't handle CSE correctly. Update to the latest stable release.

Preventing This Error Long-Term

Pre-mark your encrypted files with CSE. If you encrypt regularly, run a script on boot that applies CSE to known file extensions (.docx, .xlsx, etc.) using fsutil. I do this with a scheduled task.
Keep Controlled Folder Access on, but audit it first. Switch CFA to Audit mode via Group Policy (Computer Config > Admin Templates > Windows Components > Windows Defender Antivirus > Windows Defender Exploit Guard > Controlled Folder Access). This logs blocks without stopping them—great for testing before you go live.
Use Microsoft's recommended app list. Trusted apps like Office, Adobe, and your encryption tool should already be allowed. If you add a new one, whitelist it before the first encryption attempt.

Why I Love This Fix

Because it's one of those rare Windows errors where the solution isn't a registry hack or a driver reinstall—it's just you telling Windows "this app is fine, let it do its job." Controlled Folder Access is a lifesaver against ransomware, but it's too aggressive by default. Once you whitelist your encryption tool, error 0x00001785 vanishes for good.