LDAP error "Failed to initiate import" while trying to import users or groups

While trying to import users or groups from the Users | Settings | Configure LDAP | Users and Groups | Import Users / Groups you find the error message Failed to initiate import. 

That is happening because the authentication method on the SonicWall is not yet configured to be able to retrieve users and groups informations from the LDAP server. 

Go to Users | Settings | Configure Radius | Radius User tab, tick the option "Use LDAP to retrieve user group information". 

You can now import your users and groups from the LDAP settings.