R4 (BE 15) fails to add Linux host and establish trust with ralus

I have 2 appliances right now, respectively on R2 (BE 2012) and R4 (BE 15), and recently copied the SQL thing all the settings from the R2 one to R4 one to save loads of work after migration.

However, I discovered that the R4 cannot establish trust with one of my Linux hosts.
1. Tried upgrading the ralus agent from 14.0.1798.1373 to the newest 14.2.1180.3157: not work
2. Tried reinstalling the agent for both versions: not work
3. One of the previous posts suggested "encode=LATIN-1": not work too
4. Removed the host and can't even add it back now

But if I use R2 to re-connect it, trust can be established. Ports are allowed in the firewall since they are being used in the whole time.

Don't really know what's going on.....could anyone please help?

ralus.cfg is here, 192.168.5.14 is the IP of the R4: