Orion Web or Service logs show Solarwinds.ApiProxyFactory.TransientApiProxyException was thrown

Here is some scenario where you may encounter the same error message:

Launching the Orion Web Console being prompted with an error below:

Seen error in OrionWeb.log (C:\ProgramData\SolarWinds\Logs\Orion):

ERROR SolarWinds.Orion.Web.Filters.CatchUnhandledExceptionFilterAttribute - (null)  Error when calling action on url: http://localhost/api/ActiveAlertsOnThisEntity/GetActiveAlerts?viewId=1.
SolarWinds.ApiProxyFactory.TransientApiProxyException: Exception of type 'SolarWinds.ApiProxyFactory.TransientApiProxyException' was thrown. ---> System.ServiceModel.EndpointNotFoundException: There was no endpoint listening at net.pipe://localhost/orion/core/businesslayer that could accept the message. This is often caused by an incorrect address or SOAP action. See InnerException, if present, for more details. ---> System.IO.PipeException: The pipe endpoint 'net.pipe://localhost/orion/core/businesslayer' could not be found on your local machine.

You may have tried to add a new node to a poller or edit an existing node, you got the following error:

ERROR ApiProxy<ICoreBusinessLayer, ServiceDirectoryQuery> - (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 yourdmzape.domain.corp. ---> System.Net.Sockets.SocketException: No such host is known

You may also see this within collector logs or some other services:

ERROR ApiProxy<IAPMBusinessLayer, ServiceDirectoryQuery> - All #15 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: There was no endpoint listening at net.pipe://localhost/orion/apm/businesslayer that could accept the message. This is often caused by an incorrect address or SOAP action. See InnerException, if present, for more details. ---> System.IO.PipeException: The pipe endpoint 'net.pipe://localhost/orion/apm/businesslayer' could not be found on your local machine. 
   --- End of inner exception stack trace ---

• Mismatch of Products or hotfixes between some SolarWinds Servers
• DNS resolution failure between pollers
• System was rebooted with an incomplete Windows update
• Other issues related to the local system Environment
• Licensing Issues
• The SolarWinds Orion Core Services might be having some issues
• Services stopped

Things to check and verify: 

• Mismatch of products or hotfixes between some SolarWinds Servers
• Check DNS resolution is working between pollers in both directions
  • All the pollers should be able to resolve hostnames
  • Should also be able to Telnet on port 17777 to Main Polling Engine from the Additional Polling Engine(s) or locally
• Ensure Windows updates have completed
• Try to re-license the polling engine in question
• There is no time difference between servers
• Please follow the steps mentioned in the Basic SolarWinds Orion Troubleshooting Guide.
• Check the services in Orion Service Manager. Start the services that stopped if needed.

Also, please Check: 

• APE system requirements
• Scalability Engine Guidelines for SolarWinds Products
• Multi-module system guidelines for the Orion Platform