Okay the first error is easy enough to correct, use square brackets to access the index of an item by its string key:
ConfigurationManager.AppSettings["googlemaps.subgurim.net"]
The second error, while I understand it, I don't know the library used to wrap Google API objects well enough to know how to fix it. It's telling you to use the method directly off the library type, not of the object you've created. So try this instead:
GeoCode = Subgruim.Controles.geoCodeRequest(strFullAddress, sMapKey);
Cheers.