Endeca ENEConnectionException - How to Enable backwards compatibility, so that the Dgraph can communicate with previous versions of the Presentation API

ERROR MESSAGE in Endeca JSP reference application: ENEConnectionException com.endeca.navigation.ENEConnectionException: Error establishing connection to retrieve Navigation Engine request

Enable backwards compatibility, so that the Dgraph can communicate with previous versions of the Presentation API. In addition to the currently supported version of the Presentation API, the following previous full versions are supported: 6.0.x, 5.1.x, 5.0.x and 4.8.x. Therefore, the value for <api-version> must be one of the following:

• 601 for all 6.0.x versions of the API.
• 510 or 500 for all corresponding versions of the API, 5.1.x and 5.0.x.
• 480 for the 4.8.x versions of the API, including the Perl API. 

<dgraph-defaults>
    <properties>
     ...
    <directories>
     ...
    </directories>
    <args>
       <arg>--back_compat</arg> 
       <arg>601</arg> 
       ...
        </args>
    <startup-timeout>120</startup-timeout>
  </dgraph-defaults>

Note: Starting with version 6, the Endeca Presentation API is part of the Platform Services package. For the version of the Platform Services that is compatible with the current version of the MDEX Engine.