Credentials Doesn't Exist?
===

I'm messing about with the Bing Maps WPF control and SOAP services, trying to reverse geocode a point. I tried to implement some code from [this project][1], specifically this block of code:

    private string ReverseGeocodePoint(string locationString)
              {
                  string results = "";
                  ReverseGeocodeRequest reverseGeocodeRequest = new ReverseGeocodeRequest();
      
                  // Set the credentials using a valid Bing Maps key
                  reverseGeocodeRequest.Credentials = new GeocodeService.Credentials();
                  reverseGeocodeRequest.Credentials.ApplicationId = key;
      
                  // Set the point to use to find a matching address
                  GeocodeService.Location point = new GeocodeService.Location();
                  string[] digits = locationString.Split(';');
      
                  point.Latitude = double.Parse(digits[0].Trim());
                  point.Longitude = double.Parse(digits[1].Trim());
      
                  reverseGeocodeRequest.Location = point;
      
                  // Make the reverse geocode request
                  GeocodeServiceClient geocodeService = new GeocodeServiceClient();
                  GeocodeResponse geocodeResponse = geocodeService.ReverseGeocode(reverseGeocodeRequest);
      
                  if (geocodeResponse.Results.Length > 0)
                      results = geocodeResponse.Results[0].DisplayName;
                  else
                      results = "No Results found";
      
                  return results;
              }

However, when I try to implement it, I'm being told: `Error: The type or namespace name 'Credentials' does not exist in the namespace 'GeocodeTest.GeocodeService' (are you missing an assembly reference?)` This error occurs on the line:

    reverseGeocodeRequest.Credentials = new GeocodeService.Credentials();

Did I forgot a reference somewhere? Am I doing something incorrectly?
[1]: http://www.codeproject.com/Articles/79123/Sample-WPF-Application-Consuming-Bing-Maps-Web-Ser