Client getting Error Code: 500121 when signing into Microsoft account

Question

Hi,

I have a client who is having issues signing into their Microsoft account. This started happening last Friday where suddenly Microsoft could not verify their account.

EDIT: Image broke but you can access it here: https://i.imgur.com/MamaIj1.png

They cannot get past this screen. Even when clicking the Text option, it will not go to the screen where you enter a code.

Steps I have tried to fix the issue:

• Clear cache in browser/ Used Private browsing window
• Signed into Azure AD and cleared his phone number in MFA
• Re-required MFA and had him setup his phone number again (it would not go past the MFA setup screen)
• Waiting for 10 minutes before signing in again

Answer 1

Dear Lucilfer

Good morning! Thank you for publishing in Microsoft Community. We are happy to help you!

According to your description, generally, Error Code: 500121 indicates Authentication failed during strong authentication request. The user didn't complete the MFA prompt or they may have decided not to authenticate or timed out while doing other work, or has an issue with their authentication setup.

To resolve this issue, do one or more of the following:

• If you had selected the call option to complete the sign-in process, make sure that you respond by pressing the pound key (#) on the telephone.
• If you had selected the text option to complete the sign-in process, make sure that you enter the correct verification code.
• If you had set up other options for security verification, click Other verification options, and then try again by selecting a different option. Also, make sure that your phone numbers are correct in your user account settings.

If you still can’t access the account, please contact your Microsoft 365 tenant admin and request resetting (require re-register) MFA for you. If you are the admin, then try contacting another admin your organization for help.

In case you are the only admin in your tenant, please contact Microsoft support. We really want to help but we don’t have any resource or escalation channel to escalate this case further. Sorry for not being able to help here.

Once you reach the assisted support for the request, they will help you. The support team over there have higher permission than us, they can also contact the related team if necessary. You can contact Microsoft support via Phone. For reference, please kindly see Get support - Microsoft 365 admin | Microsoft Learn

Thank you in advance for your understanding! Your patience and cooperation will be greatly appreciated. I hope all the best!

Sincerely

Kerry Chen | Microsoft Community Moderator

Answer 2

Did you ever get this fixed? I did all of the same things and still getting the error.

Answer 3

Did you ever get this fixed? I did all of the same things and still getting the error.

I had the user signin to office.com on his phone which oddly let him in. Trying different browsers on his computer did not work however. Once signed in, I had him setup Microsoft Authenticator and he was able to login on his computer afterwards.