Error Code 500121 is a common issue faced during login attempts using the Microsoft Authenticator app, especially with Microsoft 365, Azure AD, school, or work accounts. This guide addresses the root causes of the error, offers reliable step-by-step fixes, and clarifies what to do when you’re the only admin locked out.
What Is Error 500121?
Error 500121 typically appears when multi-factor authentication (MFA) fails during the login process. According to Microsoft forums and support threads, the error is caused by:
- Denied or failed MFA prompts (e.g., tapping “Not me” in the Authenticator app)
- An expired or already-used Temporary Access Pass (TAP)
- Conditional Access Policies blocking authentication
- An incorrectly configured or outdated Microsoft Authenticator app
- Device time desynchronization, which breaks OTP code generation
Common Scenarios Where Error 500121 Appears
- You receive a prompt saying, “Enter code from Microsoft Authenticator,” but the code doesn’t show up on your app
- Your school/work account fails to log in on a new device
- You are the only administrator and get locked out
- MFA reset fails or never prompts correctly on screen
Step-by-Step Fix Guide
1. Sync Your Device Time
Incorrect system time is one of the most overlooked causes of MFA failures.
- Go to Settings > Date & Time
- Enable Automatic Time Sync
- Ensure your device is set to the correct time zone
Authenticator codes are time-based (TOTP). If your system clock is even a few seconds off, the OTP will not validate correctly.
2. Remove & Re-Add the Authenticator Account
- Open the Microsoft Authenticator app
- Tap the three dots (or long-press the account) > Remove account
- On a PC, log in to your Microsoft 365/Azure portal
- Go to Security Info or MFA settings
- Choose Add sign-in method > Authenticator app
- Scan the new QR code provided
3. Check Conditional Access & MFA Settings (Admin Only)
- Go to Azure Portal > Azure Active Directory > Users
- Click Multi-Factor Authentication in the top bar
- Check if your account is blocked
- Review Conditional Access Policies to ensure the login isn’t restricted based on device, location, or risk level
If your account was marked as a risk due to a declined MFA prompt, it could be auto-blocked under Identity Protection.
4. Reset MFA Registration (If You’re Locked Out)
If you’re unable to log in or reset MFA yourself:
- Contact your organization’s IT admin to reset your MFA settings
- If you’re the only admin:
- Try logging in with a backup admin account
- If that’s unavailable, contact Microsoft Support with your Request ID and Timestamp
5. Use Alternate MFA Methods (SMS, Call)
If Authenticator fails to prompt you:
- Visit your Security Info page
- Add an alternate sign-in method (e.g., phone number or SMS)
- Select that method during sign-in
Tip: Make sure Allow alternate methods is enabled in the MFA portal or your organization’s policy.
6. Update or Reinstall Apps
- Update both Microsoft Authenticator and Microsoft Teams (if applicable)
- Go to the App Store or Play Store and install the latest version
- If updating fails:
- Uninstall Authenticator
- Reinstall and reconfigure using fresh QR code
7. Clear Browser Cache (For Portal Access)
- Open your browser’s settings
- Clear cache, cookies, and site data
- Restart your browser and retry login
8. JavaScript & Browser Permissions
If you’re logging in via web and nothing shows:
- Ensure JavaScript is enabled
- Disable extensions that may block authentication popups
- Avoid incognito/private modes
What If You’re the Only Admin?
If you’re locked out and no one else has access:
- Use a known device and network used previously (Microsoft may allow “trusted device” fallback)
- Use password + alternate method (if previously configured)
- Contact Microsoft Support and provide:
- Error Code: 500121
- Request ID, Correlation ID, Timestamp (shown on the error screen)
Microsoft Support may offer a temporary unlock or reset TAP for admin recovery.
Additional Tips
- Use Microsoft Edge or Chrome for best compatibility
- Always back up Authenticator codes to the cloud if you’re changing devices
- Avoid tapping “Not me” unless it’s a genuine fraud alert—it may block your account
Error 500121 can feel like a dead end, especially when you’re blocked from accessing work or school accounts. But in most cases, it stems from MFA misconfiguration, expired access passes, or blocked authentication flows. With the structured fixes above—especially syncing time, re-adding your account, or resetting MFA—you can resolve the issue and regain full access.
If you’re still stuck after all steps, contact your IT team or Microsoft support with the error details.
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