I noticed your message in the Continents.py download page, so I did some investigating. The problem is that python files (at least, as used by Civ IV) cannot have a space in their name. That's why Firaxis puts "_" in their mapscript names instead of spaces (A_New_World, not A New World), and why I tend to just get rid of the spaces entirely (NorthAfrica, not North Africa, or WildWest, not Wild West). Both Hemispherical Islands and A New World in your Public Maps folder do not have spaces, and therefore, whenever I go into the Play Now or Custom Game menus I get a string of python exceptions. Inserting "_" or getting rid of the spaces entirely fixed the issue for me, and all maps showed up properly.