Error adding host

Check the 'our-solarwinds-box' server has a service listen on the IP of the engine for port 17777.

Open a command line and type this in:

netstat -na | find /i "17777"

Make sure that either it shows the IP address bound on the NIC or it binds the service to all listening IP's.  It should look like this:  0.0.0.0:17777 or xxx.xxx.xxx.xxx.:17777

If the service is running, next I would start checking to see if the windows firewall is active and stopping the in bound connection.  Turn off the windows firewall and try it again, if it works then you know that was the problem.

The firewall is not running.

netstat -na | find /i "17777"

  TCP    0.0.0.0:17777          0.0.0.0:0              LISTENING
  TCP    127.0.0.1:1789         127.0.0.1:17777        ESTABLISHED
  TCP    127.0.0.1:17777        127.0.0.1:1789         ESTABLISHED
  TCP    our-solarwinds-box:1788    our-secondary-poller:17777   ESTABLISHED
  TCP    our-solarwinds-box:2547    our-secondary-poller:17777   ESTABLISHED
  TCP    our-solarwinds-box:2591    our-secondary-poller:17777   ESTABLISHED

Perhaps I will have to open a ticket.

Last thing I can think of is that the DNS isn't working properly when it tries to resolve the hostname of 'our-solarwinds-box'. 

Try to ping the DNS name 'our-solarwinds-box' from both machines, if one fails then you know the issue.  You may need to add an entry to the windows hosts file in located C:\Windows\System32\drivers\etc with the proper resolution IP address.

Not DNS either. This just happened recently and we have not made any changes to the system. I am opening a ticket. I will post the result from that when this is resolved.

I was not on SP5 for 9.5. So we did this, and then restarted all the services. The problem cleared after this. We also noticed that this error was associated with our Custom Pollers not polling. I suspect that the issue was a simple bug and the restarting of the services corrected it.