thanks Andre
i was looking for a solution on the internet and i found this link. I think it is close to my problem.
Cloned FSMO DC- unable to create objects or register computers!
i converted two domain controllers to be virtual machines and there was a replication between them. so i think that i should check this solution first. if it wont work fine i ll try your way by migrating the FMSO roles after creating virtual machine and promoting it.