AADSTS error code 160021

Author: rwike77

articles/active-directory/develop/reference-error-codes.md

@@ -79,6 +79,7 @@ The `error` field has several possible values - review the protocol documentatio
 | AADSTS16000 | SelectUserAccount - This is an interrupt thrown by Azure AD, which results in UI that allows the user to select from among multiple valid SSO sessions. This error is fairly common and may be returned to the application if `prompt=none` is specified. |
 | AADSTS16001 | UserAccountSelectionInvalid - You'll see this error if the user selects on a tile that the session select logic has rejected. When triggered, this error allows the user to recover by picking from an updated list of tiles/sessions, or by choosing another account. This error can occur because of a code defect or race condition. |
 | AADSTS16002 | AppSessionSelectionInvalid - The app-specified SID requirement wasn't met.  |
+| AADSTS160021| AppSessionSelectionInvalidSessionNotExist - Application requested a user session which does not exist. |
 | AADSTS16003 | SsoUserAccountNotFoundInResourceTenant - Indicates that the user hasn't been explicitly added to the tenant. |
 | AADSTS17003 | CredentialKeyProvisioningFailed - Azure AD can't provision the user key. |
 | AADSTS20001 | WsFedSignInResponseError - There's an issue with your federated Identity Provider. Contact your IDP to resolve this issue. |