TO create a Child domain Unders the Domain Tree

Hello Everybody ,

I  have Created a New Forest name is Labs.com.  SO labs.com is  my Forest and Tree Name .

NOw under that i created a New Child Domain  as  Sales.Labs.com

Then I Created a New Domain Tree in Existing Forest as Test.com .

now i want to create a Child DOmain under this new Domain Tree Test.com ( as HR.Test.COm)

i am unable to do that .  it gives me an error

 " The Operation Failed because.....Active Dir Domain Serives Could not create The Object cn=hr,cn=partitions,cn=configuration,dc=labs,dc=com....  Could not access a Partition of the Dir Service Located on a remove Server.Make Sure at least one server is running for the Partition in question "

I know to add Child domain or new domain tree u must be an Enterprise Admin.

Need Help. plizz give ur suggestions

Yunus.