When you record a GWT application with NeoLoad, it will try to convert the binary GWT data to an XML format. 

To do so, you have to load in NeoLoad the JAVA classes used by your application. They are available in your server where the application is deployed.

That ****.gwt.rpc files are some of the needed files. New files are created each time a new build of your application is created.

You should contact the developers of your application to get them.

For more information, see that GWT tutorial from the NeoLoad documentation here