How to Fix Microsoft 365 Error Code 500121 After Removing MFA
Question details
The user needs to regain access to a Microsoft 365 administrator account that fails to sign in and displays error code 500121.
- Product
- Microsoft 365
- Device & OS
- not provided
- Scenario
- Attempting to sign in to a Microsoft 365 admin account after manually deleting the associated phone number and Microsoft Authenticator methods.
- Observed behavior
- The system blocks the sign-in process and prompts error code 500121 because the required multifactor authentication methods are missing and cannot be completed.
Determine whether there is another global administrator account active within your Microsoft 365 tenant, as admin privileges are required to reset authentication methods for locked users.
Reset MFA Settings via Another Administrator Account
If your organization has multiple administrators, a secondary admin can easily reset your multifactor authentication settings from the admin center.
This is the fastest method to regain access. It bypasses the lockout by completely clearing the broken MFA requirement, allowing you to re-register your phone or Authenticator app upon your next login.
Have the secondary administrator sign in to the Microsoft 365 admin center using their credentials.
Go to 'Users' and select 'Active users' from the left-hand navigation pane.
Locate and click on your locked administrator account to open the account properties.
Click on 'Manage multifactor authentication' and choose the option to clear or reset the existing MFA settings for the locked user.
Contact Microsoft Data Protection Support
Use this solution if you are the sole global administrator in your organization and are completely locked out of the tenant.
Clear Browser Cache and Cookies
Perform a browser reset to ensure that stale cached credentials or login loops are not contributing to the error.
Avoid Cloud Lockouts with Offline-Friendly WPS Office
While Microsoft 365 relies heavily on strict cloud authentication policies that can lead to lockouts, WPS Office offers a powerful, lightweight alternative that allows you to work seamlessly both offline and online. Enjoy a highly familiar interface and excellent compatibility with Microsoft file formats without the hassle of complex mandatory cloud logins.
- 1. Download WPS Office: Visit the official WPS website to download and install the free software.
- 2. Open Microsoft Formats: Open your existing .docx, .xlsx, and .pptx files directly; no format conversion is necessary.
- 3. Edit Offline: Start editing your documents immediately without needing to authenticate through a cloud service.
Frequently Asked Questions
What causes Microsoft 365 Error Code 500121?
This error occurs when the multifactor authentication (MFA) process fails. It is most commonly triggered because the configured authentication method, such as a phone number or the Microsoft Authenticator app, was removed, disabled, or is otherwise unreachable during sign-in.
Can I bypass the 500121 error by clearing my browser cache?
Clearing your browser cache can resolve basic login loops caused by stale authentication tokens. However, it will not bypass the error if you have genuinely deleted your only configured MFA method; you will still need an administrator to reset your MFA.
What should I do if I am the only global admin and get locked out?
If you are the sole global administrator for your tenant and lose MFA access, you cannot fix it yourself. You must contact the Microsoft Data Protection support team by phone to securely verify your identity and have them manually restore your access.
How can I prevent being locked out of my admin account in the future?
To prevent tenant-wide lockouts, Microsoft highly recommends setting up a 'break-glass' or emergency access administrator account. This account should be highly secured but specifically excluded from the strict MFA conditional access policies applied to your daily admin accounts.
