getting error on Azure server when trying to download more than 1 file from box.com

I am getting this error below when trying to download more than 1 file from box.com using c# code.

Here is my code:

var config = new BoxConfig(CLIENT_ID, "", uri);
var session = new BoxJWTAuth(config);
var client = session.AdminClient(apptoken);

var folderId = ConfigurationManager.AppSettings["FolderID"]; // "0";//
var folder = await client.FoldersManager.GetInformationAsync(folderId);
folderName = folder.Name;
var localFolderPath = Path.Combine(downloadFolderName, folderName);
ResetLocalFolder(localFolderPath);

var items = await client.FoldersManager.GetFolderItemsAsync(folderId, 1000, autoPaginate: true);

var fileDownloadTasks = new List();
var files = items.Entries.Where(i => i.Type == "file").ToList();

foreach (var file in files)
{
var t = await client.FilesManager.DownloadAsync(file.Id);
using (var localFile = File.Create(Path.Combine(localFolderPath, file.Name.Replace(":", ""))))
{
t.CopyTo(localFile);
}
}

foreach (var file in files)
{
fileDownloadTasks.Add(client.FilesManager.DeleteAsync(file.Id));
}

await Task.WhenAll(fileDownloadTasks);

Here is the error i get.

One or more errors occurred. at System.Threading.Tasks.Task.ThrowIfExceptional(Boolean includeTaskCanceledExceptions)
at System.Threading.Tasks.Task.Wait(Int32 millisecondsTimeout, CancellationToken cancellationToken)
at System.Threading.Tasks.Task.Wait()