正在将大文件上载到azure blob

我正在使用以下程序将大文件上传到azure blob存储。当上传一个小于500KB的小文件时，程序在其他情况下运行良好我在下面的行中得到一个错误：

blob.PutBlock（blockIdBase64，stream，null）
as"Microsoft.WindowsAzure.Storage.dll中发生了类型为"Microsoft.WindowsAzure.StorageException"的未处理异常附加信息：远程服务器返回错误：（400）错误请求"

没有关于这个例外的细节，所以我不确定问题出在哪里。关于以下程序中可能出现的错误，有什么建议吗：

class Program
    {
    static void Main(string[] args)
    {
    string accountName = "newstg";
    string accountKey = "fFB86xx5jbCj1A3dC41HtuIZwvDwLnXg==";
    // list of all uploaded block ids. need for commiting them at the end
    var blockIdList = new List<string>();
    StorageCredentials creds = new StorageCredentials(accountName, accountKey);
    CloudStorageAccount storageAccount = new CloudStorageAccount(creds, useHttps: true);
    CloudBlobClient client = storageAccount.CreateCloudBlobClient();
    　
    　
    CloudBlobContainer sampleContainer = client.GetContainerReference("newcontainer2");
    string fileName = @"C:'sample.pptx";
    CloudBlockBlob blob = sampleContainer.GetBlockBlobReference("APictureFile6");
    using (var file = new FileStream(fileName, FileMode.Open, FileAccess.Read))
    {
    int blockSize = 1;
    // block counter
    var blockId = 0;
    // open file
    while (file.Position < file.Length)
    {
    // calculate buffer size (blockSize in KB) 
    var bufferSize = blockSize * 1024 < file.Length - file.Position ? blockSize * 1024 : file.Length - file.Position;
    var buffer = new byte[bufferSize];
    // read data to buffer
    file.Read(buffer, 0, buffer.Length);
    // save data to memory stream and put to storage
    using (var stream = new MemoryStream(buffer))
    {
    // set stream position to start
    stream.Position = 0;
    // convert block id to Base64 Encoded string 
    var blockIdBase64 = Convert.ToBase64String(Encoding.UTF8.GetBytes(blockId.ToString(CultureInfo.InvariantCulture)));
    blob.PutBlock(blockIdBase64, stream, null);
    blockIdList.Add(blockIdBase64);
    // increase block id
    blockId++;
    }
    }
    file.Close();
    }
    blob.PutBlockList(blockIdList);
    }
    }

var blockIdBase64 = Convert.ToBase64String(Encoding.UTF8.GetBytes(blockId.ToString("d6", CultureInfo.InvariantCulture)));