A referral was returned from the Server

1) I have one Domain Controller
"VM2008R2DC.xyz.com". And a domain joined
computer "VM2008R2Dirsync.xyz.com" in which "Dirsync" is working perfectly.

2) I have installed one more Child Domain
"VM2008R2DC2.child.xyz.com".

3) When I try to run Dirsync tool with child's
administrator credential, I get the following error -

Configuration error

User CHILD\Administrator is not a member of the group ENterprise Admins.
Add this user to this group, and then try again.

4) When I try to add "Enterprise Admins" as a
"Member of", I get the following error -

The following Active Directory Domain Services error occured: A referral
was returned from the server.