If the Agent was removed, you may receive this error when adding the Agent back to replication:
“This agent has already been replicated to the remote slave core”
The agent was added at some point to replication but when the agent was removed, the agent registry settings remained.
This issue can also be caused by a replication link deleted manually from the registry.
To resolve the issue, please perform the following steps:
1. Stop the source core service
2. Open regedit
3. Navigate to: HKEY_LOCAL_MACHINE\SOFTWARE\AppRecovery
4. Export the key to the desktop for a backup copy
5. Navigate to: HKEY_LOCAL_MACHINE\SOFTWARE\AppRecovery\Core\Agents\”Problem agent ID”\ReplicationService\AgentRemoteSlaveCoreSettings\0
6. Remove the registry key 0
7. Start the source core service
8. Add agent to replication