Creating Help Pages for ASP.NET Web API and Documenting Return types

Question

For creating Help page for API methods, xml documetation has been used as this Creating Help Pages for ASP.NET Web API and ASP.Net WebApi Help Page have described. One of my api's signature is like this :

        /// <summary>
        ///  this is getting a place's information
        /// </summary>

        /// <param name="placeKey">Unique key of place</param>
        /// <param name="checkIn">Checkin date </param>
        /// <param name="checkOut">CheckOut date </param>
        /// <returns>
        ///        Place's Information
        /// </returns>
    Core.Services.APIViewModels.PlacesViewModel GetPlaceInformation(string categoryKey, string placeKey, string checkIn , string checkOut)

The xml documentation is correct, except that we need to document the PlacesViewModel return type. Actually the PlacesViewModel is a view model in another of project in solution. xml comments has been provided for it like here :

    /// <summary>
    /// a place information.</summary>   
    public class PlacesViewModel
        {
        /// <summary>
        ///unique number of place</summary>
        public long PlaceId { get; set; }
        /// <summary>
        ///  place's name</summary>
        public string PlaceName { get; set; }
        /// <summary>
        /// places's key</summary>
        public string Key { get; set; }
}

But it doesn't work and PlacesViewModel class attend in help page with empty value for Description's column in the table of PlacesViewModel as if there is no xml comment for them. How come can be provided a documentation for PlacesViewModel

If the PlacesViewModel move to the same project, it will work well!