Since June 22nd Google requires an API key in order to use its mapping features. That is for domains that started using the maps services after June 22nd. Domain that have been using the maps services before June 22nd can keep using the features without an API key. That is why you get the error on the new domain. You can read more about it here.
You can easily create an API key ( it is free ) and enter it in the settings page of GEO my WP plugin.