C#.NET reports "The request failed with HTTP status 401: Unauthorized" when accessing

We've recently seen an issue where C#.NET reports "The request failed with HTTP status 401: Unauthorized" when accessing a classic SOAP Web Reference.

The credentials are set using  CredentialCache.DefaultCredentials as shown in the code below.

/// <summary>

/// Starts the service.

/// </summary>

/// <remarks>The scheduler web service is not polled at start-up to improve start response times.</remarks>

public void StartService()

{

    try

    {

        server = new XIAAutomation();

        server.Credentials = CredentialCache.DefaultCredentials;

        server.Url = GetWebServiceUrl();

        server.Timeout = 60000;

        SetupTimer();

        Diagnostics.WriteEvent(String.Format(Resources.Service.StartupComplete, Assembly.GetExecutingAssembly().GetName().Version, server.Url), EventLogIdentifiers.Startup);

    }

    catch (Exception ex) { Diagnostics.WriteEvent(Resources.Service.StartupFailedException, EventLogIdentifiers.Startup, ex); }

}

 
The solution to this problem is to ensure that  the credentials are set after the URL

       

server.Url = GetWebServiceUrl();server.Credentials = CredentialCache.DefaultCredentials;