⚠️ 2 verified solutions available for Error 4421 — Last updated 2026-02-23
Error 4421 📋

Fix ERROR_SECUREBOOT_POLICY_VIOLATION — Windows Error Code 4421

Error 4421 (ERROR_SECUREBOOT_POLICY_VIOLATION) is a Windows DNS & WINS error that occurs when the value is protected by secure boot policy and cannot be modified or deleted.. This guide provides step-by-step solutions to resolve this issue.

🏷️ Code: 4421 📛 ERROR_SECUREBOOT_POLICY_VIOLATION 📅 Updated: 2026-02-23 ⏱️ 2 Solutions
⚡ Quick Fix

Flush DNS and Switch Servers: Open Command Prompt as Administrator

👇 See all 2 solutions below
🐞 Auto-Fix Script for Error 4421
⚠️ How to use: Open PowerShell as Administrator, paste the code above, and press Enter.
✓ Safe & Transparent ✓ No Downloads Required ✓ Review Before Running
📑 Table of Contents
What is Error 4421? Common Causes Step-by-Step Solutions Prevention Tips Related Errors

💡 What is Error 4421?

Windows System Error Code 4421, known as ERROR_SECUREBOOT_POLICY_VIOLATION, is a DNS & WINS error that occurs during DNS resolution and WINS name resolution. The error indicates that: The value is protected by Secure Boot policy and cannot be modified or deleted. When this error is encountered, the Windows operating system was unable to complete the requested operation within the DNS/WINS services subsystem. The error code 4421 is returned by the GetLastError() function and provides developers with a specific identifier to diagnose the root cause of the failure. The symbolic name ERROR_SECUREBOOT_POLICY_VIOLATION maps directly to this numeric code and is commonly referenced in Microsoft documentation, developer forums, and system logs. Understanding this error and its context within DNS resolution and WINS name resolution is essential for effective troubleshooting.

⚠️ Common Causes

  • System resource conflict: The value is protected by Secure Boot policy and cannot be modified or deleted.
  • DNS server misconfigured
  • Stale DNS cache entries
  • Hostname cannot be resolved
📚 Comprehensive Guide

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A comprehensive guide on Component Object Model (COM), Distributed COM (DCOM), and how to safely interpret and resolve Event ID 10016 errors.

Read the full guide →

✅ Step-by-Step Solutions

1 Flush DNS and Switch Servers
  1. Open Command Prompt as Administrator
  2. Run: ipconfig /flushdns
  3. Change DNS to Google (8.8.8.8) or Cloudflare (1.1.1.1)
  4. Run: ipconfig /registerdns
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Show Advanced Solutions (1 more)
2 Advanced Diagnostic for ERROR_SECUREBOOT_POLICY_VIOLATION
  1. Open Windows Event Viewer (eventvwr.msc)
  2. Navigate to Windows Logs → System to find Event ID 4421
  3. Look for associated warnings that occurred immediately before the system crashed
  4. Right-click the entry and export the log file for further analysis

🎬 Video Tutorials

▶️ Watch Video Tutorials
How to fix Error 4421 (Secureboot Policy Violation)
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💻 Diagnostic Command

Run this PowerShell command to find related events in your system log:

Get-EventLog -LogName System -Newest 20 | Where-Object {$_.Message -like "*4421*" -or $_.Message -like "*ERROR_SECUREBOOT_POLICY_VIOLATION*"} | Format-List

💡 Open PowerShell as Administrator, paste the command above, and press Enter.

🛡️ Prevention Tips

  • Use reliable DNS (8.8.8.8 or 1.1.1.1)
  • Flush DNS cache periodically
  • Monitor DNS resolution performance
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Last updated: 2026-02-23
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Based on Official Microsoft Documentation
Solutions Tested on Windows 10 & 11
Error codes sourced from Microsoft Win32 SDK. Updated 2026-02-23.
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