We have examined the log and here are our findings:
In fact everything goes fine in the log except for the last error in secondary and primary FTP server
2013-10-07 12:06:11.223 INFO Ftp(1) Response: 435 Failed TLS negotiation on data channel (using SSL accept()), disconnected
2013-10-07 12:06:11.223 INFO Ftp(2) Response: 435 Failed TLS negotiation on data channel (using SSL connect()), disconnected: Success.
Both the servers have notified Rebex FTP client about these error, but we cannot read anything more from it than reported by the servers...
We do not have (and cannot possibly find out from the Rebex FTP client point of view) why the negotiation between the two servers has failed.
One possible way to find this piece of information is to look into the actual FTP server logs.
Could you also try if the FXP between those two servers works with another FTP client? (e.g. FlashFXP has support for FXP).
If you can make FXP work with another FTP client, please create the log of the communication and send it to us.