1 ERG server, 2 Management servers
How many ERG servers do you have? Are you running the installer twice on the same server to connect to both management servers?
Also, the ERG installer is not reusable for multiple servers. You need to download a new one for each install.
If you will be using a load balancer, you should be putting the load balancer's address during the ERG install.
I think I have found the solution. If you have more than one Management Server it is important that they all are reachable via the same "Management Service Address" FQDN.
Then you can download the ERG file from web console and extract it on ERG server by using the Management Service Address.