For the succesful replication of the database between Primary and Secondary ACS server, refer to this checklist:
On Primary ACS server:
You must have the AAA server entry for Primary and Secondary server(s) in the Network Configuration > AAA server section.
You must have the same shared key for both entries Primary and Secondary ACS Server(s).
In the Replication column in System Configuration > Internal Database Replication, the ACS must have the entry of all the secondary servers that ACS wants the replication information to
be sent.
On Secondary ACS server(s):
You must have AAA server entry for Primary and Secondary server(s) in Network Configuration > AAA server section.
You must have the same shared key for both entries Primary and Secondary ACS Server(s).
In the Replication column in System Configuration > Internal Database Replication, there should not be any entry there. It should be empty.