Is there any difference in ENEQuery object between Endeca 5 and Endeca 6?

I am trying to integrate some code written for Endeca 6 to a codebase that queries a Endeca 5 server. I got exceptions: Navigation Engine not able to process request

I am using the code like this:

 l_oQueryResults = getSearchConnection().getConnection(pRequest.get(SearchRequestBean.Locale)).query(pEneQuery);

I think theoretically if I pass the right pEneQuery, I can query the Endeca 5 indexes, right? So I am wondering if I passed a correct pEneQuery that can be identified by Endeca 5 navigation lib.Do you have any ideas?

The issue is probably with the endeca_navigation.jar being the wrong version. You need to make sure that you use the endeca_navigation.jar that comes with Platform Services 5.X.

absolutely - there is a difference even among minor versions of their API (.jar or .dll). The version of your application API must match the mdex server's API version.