You’re seeing Error Code 500121—this typically relates to a Multi-Factor Authentication (MFA) failure during login, particularly when using the Microsoft Authenticator app, Microsoft 365, Azure AD, or similar services.
What Does Error 500121 Mean?
This error indicates that authentication failed during the MFA prompt—common causes include:
You declined the verification request (e.g., tapped “Not me”).
You didn’t complete the MFA prompt in time.
Your device clock is out of sync, invalidating time-based codes.
A Conditional Access policy or security setting blocked the sign-in.
Your account is temporarily blocked or marked high-risk by security policies.
What Users and Microsoft Documentation Reveal
From Microsoft Community:
If you used phone verification, ensure you press
#to confirm.For SMS, input the correct code.
Try other sign-in methods if available and confirm your registered phone numbers are correct.
For business/education accounts, ask your admin to reset/re-register MFA if you’re locked out. If you’re the sole admin, you may need to contact Microsoft Support.
Real-World Examples & Risks:
Tapping “Not me” in the Authenticator app can trigger an automatic block due to fraud alerts—this block may last up to 90 days unless manually unblocked by an admin.
Excessive rejected MFA attempts (error 500121) might indicate a potential security threat—tools like Splunk can flag such behavior for investigation.
Also Read : babyoftheyear.org Scam
Fixes & Next Steps
| Step | What to Do |
|---|---|
| 1 | Ensure device time is accurate – enable automatic sync with correct timezone on your phone. |
| 2 | Re-register your Authenticator – remove the account from the app, reset MFA via your Microsoft Security Info page, then scan a new QR code. |
| 3 | Try a different MFA method – use SMS, call, or another verification method if available. |
| 4 | Check Conditional Access policies – reach out to your IT admin to confirm nothing is blocking your login attempt. |
| 5 | Unblock the account if needed – especially if the block was triggered by fraud alerts; admin can clear it via the Microsoft Entra (Azure AD) portal. |
| 6 | Contact Support – if you’re the only admin or still can’t access your account, reach out to Microsoft Support with your error details. |
Summary in Plain Terms
Error 500121 means your MFA failed—either because you dismissed the prompt, your device settings are off, or a security policy blocked it.
To fix it:
Save time by syncing your device clock.
Re-register your MFA method.
Try a different verification method if needed.
Work with your admin to ensure nothing is blocking the login.
If blocked, have them unblock your account.
As a last resort, reach out to Microsoft Support.
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