Try adding the [Invoke] attribute to your InitUserSettings method:
[Invoke]
public InitUserSettingsDTO InitUserSettings(Guid userId)
{
var initUserSettingsDTO = new InitUserSettingsDTO();
return initUserSettingsDTO;
}
Make sure your web.config is set up as described here: http://msdn.microsoft.com/en-us/library/ff426912(v=vs.91).aspx