Unable to Add, Edit or List Resource for nodes assigned to an Additional Polling Engine with error (SolarWinds.ApiProxyFactory.TransientApiProxyException)

When adding, editing or Listing Resources for all Nodes polled by an Additional Polling Engine, the following issue is presented "SolarWinds.ApiProxyFactory.TransientApiProxyException"
 

• WARN and ERROR seen in the OrionWeb.log from the Main Polling Engine (C:\ProgramData\SolarWinds\Logs\Orion):

WARN  SolarWinds.Orion.Core.SharedCredentials.OrionEntitySharedCredentialManager`1 - (null)  Found no CredentialRelations records for entity Uri swis://<ServerName>/Orion/Orion.Nodes/NodeID=531 and use PaloAltoFirewall

ERROR ApiProxy<ICoreBusinessLayer, ServiceDirectoryQueryInternal> - (null)  All #3 
retries calling an API channel from a pool 'RootPool' failed due to a transient error detected.
SolarWinds.ApiProxyFactory.TransientApiProxyException: Exception of type 'SolarWinds.ApiProxyFactory.TransientApiProxyException' was thrown. ---> System.ServiceModel.EndpointNotFoundException: No DNS entries exist for host APE_Hostname. ---> System.Net.Sockets.SocketException: No such host is known

or
 

ERROR ApiProxy<ICoreBusinessLayer, ServiceDirectoryQueryInternal> - (null)  All #3 retries calling an API channel from a pool 'RootPool' failed due to a transient error detected.
SolarWinds.ApiProxyFactory.TransientApiProxyException: Exception of type 'SolarWinds.ApiProxyFactory.TransientApiProxyException' was thrown. ---> System.ServiceModel.EndpointNotFoundException: Could not connect to net.tcp://inkeosolar0001.ad001.siemens.net:17777/orion/core/businesslayer. The connection attempt lasted for a time span of 00:00:01.0313300. TCP error code 10061: No connection could be made because the target machine actively refused it 19.1.1.1:17777.  ---> System.Net.Sockets.SocketException: No connection could be made because the target machine actively refused it 19.1.1.1:17777
   at System.Net.Sockets.Socket.DoConnect(EndPoint endPointSnapshot, SocketAddress socketAddress)
   at System.Net.Sockets.Socket.Connect(EndPoint remoteEP)
   at System.ServiceModel.Channels.SocketConnectionInitiator.Connect(Uri uri, TimeSpan timeout)
   --- End of inner exception stack trace ---

• The hosts file on the Main Polling Engine (C:\Windows\System32\drivers\etc) has an incorrect IP Address or missing information.
• Port 17777 is not open bidirectional between the Main Poller and Additional Poller.

Solution 1 

Update the hosts file of the Main Polling Engine and Additional Poller according to its necessity (C:\Windows\System32\drivers\etc).

Solution 2

Test port 17777 from both Main Poller and Additional Poller to make sure they are open bidirectional according to the article SolarWinds Port Requirements - Additional polling engine

1. Open PowerShell with administrator privileges and enter the following command, replacing '<IP_ADDRESS>' with the IP address from the Main or Additional Poller.

tnc <IP_ADDRESSS> - Port 17777