Because this property editor uses Google Maps you need to get an API key. Once you have an API key, under Global Settings, add the API key with the name of GoogleMaps
public class GoogleMapPosition
{
/// <summary>Gets or sets the latitude.</summary>
/// <value>The latitude.</value>
public double Lat { get; set; }
/// <summary>Gets or sets the longitude.</summary>
/// <value>The longitude.</value>
public double Lng { get; set; }
}