I am getting the same error.
Could you solved the problem? If yes, How?
Have you tried typing "NitroStarted" on the console # prompt (e.g. <HOSTNAME>#) this will give you the status of the ESM. Then you can type "NitroStart --nod" to restart the ESM, then tail the /var/log/messages file to review the progress and/or errors.
After nearly two years since posting, I'm marking the OP's post as "Assumed Answered".
I solved the problem for now. I stopped and startted the Receiver from ESM console. The problem is gone. But I couldnt find the real reason for that.
How did this happend;
I added the DNS client as log source via v10 SIEM collector. v10 works 8081 port on default (MEF port). I changed the port on collector and ESM console(log source list- interface)
That error showed up.