I just had a quick look at the download package, but its chock-full of stuff! Are you sure that there are no custom Resources or Terrain or anything included in the WBS only map? Because you're not supposed to load the map directly, but rather load the GEM mod firstly, then load the map included in the mod.
What you basically need to do is mod the GEM mod. It seems that you can't simply lift the WBS out of its context and apply it to your own personal mod. So your mod will be a mod-mod of GEM, then.
I suggest you ask for advice on the GEM sub-forum - the folks over there should be able to help you out, whatever it is you plan on doing.
edit: GEM includes a custom DLL file, for crying out loud!