event_log showed the error like "Export cannot connect to import on the destination system"
The root cause of the problem was that the source-side paramdb was set to use ssh tunnels to the targets, but the ssh tunnel processes on the source system were not running.
Please check paramdb file on the source and target to see if there is any setting for SSH, if so, comment it out.
If custome is doing replication in SSH environment. It is required for ssh tunnels running and be visible in the ps -ef display. The tunnel commands, and the corresponding ps -ef entries, would look similar to:
ssh -L <port>:destination_host_name