'Unauthorized' error in .net webservices developed in C#

The request failed with HTTP status 401: Unauthorized. Why?

TravelCodesTranslator ws = GetEncodeDecodeWS();

// Create and set up the credentials for XmlSelectWebService
 string UserName = "username";
 string Password = "pwd";
// Xml Select uses Basic Authentication
NetworkCredential credentials = new NetworkCredential(UserName, Password);
CredentialCache cc = new CredentialCache();
ws.PreAuthenticate = true;
ws.Credentials = credentials;

XmlElement response;

if (_requestType == "Encode")
{
    response = ws.Encode(request.DocumentElement); // got error of
                                                   // "The request failed
                            开发者_开发问答                       //  with HTTP status 401:
                                                   //  Unauthorized."
}
else
{
    response = ws.Decode(request.DocumentElement);
}

Change

ws.Credentials = System.Net.CredentialCache.DefaultNetworkCredentials;

to

ws.Credentials = credentials 

Tip: The error message is quite clear. It says your credentials are not correct. Then I would check whether the username and password are correct. If they are correct then I would see if they are assigned properly to the request.