What Does Error Code 500121 Mean?

Error code 500121, often associated with Microsoft services like Microsoft 365, Azure AD (now Microsoft Entra ID), and the Microsoft Authenticator app, indicates a Multi-Factor Authentication (MFA) failure during a strong authentication request. This means a secondary verification step is required, but it's not being completed successfully, according to Microsoft Community.

Possible causes

• Failure to complete the MFA prompt: The user might ignore, time out, or cancel the prompt from the Authenticator app, says Microsoft.
• Incorrect code entry: If using a verification code, the entered code might be incorrect.
• MFA setup issues or misconfiguration: There might be a problem with the way MFA is set up on the account.
• Time mismatch between the device and server: The device's time and date settings might not be synchronized with the server, leading to problems with code generation in the Authenticator app.
• Conditional Access policies: The sign-in attempt might be blocked by a Conditional Access or MFA block policy in Azure AD/Microsoft Entra ID, notes Azure.cn.

Troubleshooting steps

Several steps can help resolve error 500121:

• Check your MFA method: If using the Authenticator App, ensure it's open and connected to the internet. For SMS or phone calls, confirm the registered number is correct and has good signal.
• Try an alternative MFA method: If available, use the "Sign in another way" option.
• Evaluate network restrictions: If signing in from a new location, try a trusted network as organizational policies might be the cause.
• Clear browser data: Old session information in your browser's cache and cookies can interfere with MFA.
• Ensure device time is synchronized: Set your device's date and time to automatic. For Android users, use the "Time correction for codes" feature in the Authenticator app settings.
• Verify the correct account: If you have multiple accounts, confirm the correct Microsoft account is selected in the Authenticator app.
• Manage accounts in Authenticator: Removing and re-adding your account to the Authenticator app using a new QR code can help resolve sync issues.
• Update applications: Ensure both the Microsoft Authenticator app and the application you're trying to access are updated. Reinstalling them might also help.
• Contact IT support: If these steps don't work, contact your IT administrator or Microsoft 365 Admin. Provide them with the error code, Request ID, Correlation ID, and Timestamp to assist with diagnosis using Azure AD sign-in logs. They can adjust policies or reset MFA. If you are the sole administrator and cannot log in, you may need to contact the Data Protection team.

Resolving this error often requires administrator intervention, especially for issues related to Conditional Access policies or MFA resets.