Please Help me !! Can not create object in AD.

[The One]

When I create any object in AD I receive popup
message "Windows cannot validate the uniqueness of this
proposed user name with a global catalog server because:
The server is not operational. Windows will create this
user account, but the user can log on only after the user
name is verified to be unique."

and in Event viewer -> Directory Service has error "Unable
to establish connection with global catalog."
Event ID : 1126
and the error occur every hour.

Please help thanks.

 

[Jason Robarts [MSFT]]

Can you ping your GC? If the GC is up, a common reason for this problem is
a DNS issue. You should verify the primary and secondary DNS servers the
machine you are seeing this problem on can resolve the _gc records for your
GC.

Have you recently demoted a DC? Was it a GC?

Jason