I am getting 401 unauthorized error on webclient.openread(url) in sharepoint onlin

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SharePoint

C#6.0

Hi,

I am getting 401 unauhtorized issue,when I try to execute this "Stream stream = webClient.OpenRead(imageInformation.Url)" line;

I am giving the full piece of code for your reference.

using (WebClient webClient = new WebClient())
            {
                webClient.Credentials = new SharePointOnlineCredentials(ConfigSettings.VNextSiteUsername, password);
                webClient.Headers.Add(CommonConstants.Authentication, "f");

                if (imageInformation.Url != null)
                {
                    Stream stream = webClient.OpenRead(imageInformation.Url);

                    Bitmap bitmap = new Bitmap(stream);
                    stream.Flush();
                    stream.Close();
                    Directory.CreateDirectory(ConfigSettings.DownloadPath);
                    bitmap.Save(ConfigSettings.DownloadPath + imageInformation.GPNNumber + '.' + imageInformation.Extension);
                    Console.WriteLine("Profile pictures downloaded to local - " + imageInformation.GPNNumber + '.' + imageInformation.Extension);
                }
            }  


Please help me.

What I have tried:

I have tried disabling my proxy settings
I have checked my credentials also
It was working till now,all of a sudden after a month it is not working