Systems Deployment

I'm having problem with Automatic Setup using RIS across a child domain. When I use RIS within the domain, automatic setup works fine, it recognize the computer account exist and re-install using the computer name. When I relocate the client account location to a child domain, RIS automatic setup does not see the computer account exist and kept creating new accounts (test1, test2,test3,etc..). I even give full control permission to the OU and computer account to the account that I login to the RIS. Any suggestion? Thanks