Exception return from FlightInfoStatus API

I keep getting “{“The data contract type ‘FlightawareServiceReference.ArrayOfFlightInfoStatusStruct’ cannot be deserialized because the required data members ‘PropertyChanged, flightsField, next_offsetField’ were not found.”}”
when trying to deserialize the result.
have any idea why and what to do?

Here is the code -
private const string fxmlUrl = “http://flightxml.flightaware.com/json/FlightXML3”;
private const string username = “MYUSERNAME”;
private const string apiKey = “MYAPIKEY”;
private static UriBuilder uriBuilder = new UriBuilder(fxmlUrl);

public static void GetFlightData(string flightName)
    var requestUrl = fxmlUrl.AppendPathSegment("FlightInfoStatus")
            .SetQueryParams(new { ident = "CAP85" });
    ProcessRepositories(requestUrl, username, apiKey).Wait();

private static async Task ProcessRepositories(string apiUrl, string username, string apiKey)
    var serializer = new DataContractJsonSerializer(typeof(ArrayOfFlightInfoStatusStruct));
    var client = new HttpClient();
    var credentials = Encoding.ASCII.GetBytes(username + ":" + apiKey);
    client.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue("Basic", Convert.ToBase64String(credentials));

    var streamTask = client.GetStreamAsync(apiUrl);
        var arrayOfFlightInfoStatusStruct = serializer.ReadObject(await streamTask);// as ArrayOfFlightInfoStatusStruct;
    }catch(Exception e)