I have just purchased a product called AD Manager from Manage Engine. Good stuff but I am facing a very unique problem. I have one parent and 3 child domains. When I create a user in the parent domain and then I try to create the same user in the child domain (they have the same UPN), it allows me to do so. However when I try to do this through the AD directly, there is an error message. I don’t understand how the AD Manager Solution is not able to find the same user and is able to create a duplicate user with the same UPN.