I am not able to replicate Database between two ACS SE 4.2. I am getting the following error:
Inbound database replication from ACS 'ACS_BEX_001' denied - shared secret mismatch.
The configuration apparently is ok. I am attaching the configuration from both ACS.
The problem you are seeing is because of the Self entries on each ACS being set to 127.0.0.1. For replication to work you have to set all 4 ACS entries to the same shared secret, even the Self ones. The issue is when you try to change those entries it will tell you that you can't use 127.0.0.1, but it also won't let you change the ip.
The bug Id for this issue is CSCso36620. The workaround states that from the CLI you can use the 'set ip' command to set the IP back to the original IP and it should update the Self entry in the gui. At that point you should be able to update the shared secret on all 4 devices.
Let me know if you have any problems getting that to work.