When you export your project from Unity to XNA, it is done using a Unity script 'ExportSceneWizard' - that makes all the menus, and a DLL that holds all the code to write the XML.

Problems with getting XNA to compile the XML

The source code for the exporter is in the Exporter folder of the project. If you find yourself in a situation where you have problems with getting your XML files to compile in XNA, it is probably because your exporter is out of date. To update it, just open the PressPlay.FFWD.Exporter project in Visual Studio and compile it. This should copy a new, update version of the Exporter DLL to the Unity project. After that a reexport from Unity will fix the errors.