If you are getting an error that the new authentication method isn't working with your account and that the protocol is being reverted, it means you are unable to decrypt your account's private key.
Every account has a public key and a private key that is encrypted on the client with the user's password. In the new authentication protocol, we use the public key for a more secure token delivery, such that the token is never sent across explicitly and can only be decrypted by the holder of the private key.
When the above error occurs, it means that the key pair stored on our servers is deprecated and the password can no longer decrypt the private key. To avoid further issues with OTP reprompts, we recommend you contact BitGo support if you ever see the error.