403错误SignatureDoesNotMatch

<DIV id=read_tpc mb10?>FileStream theFileStream = new FileStream(filePath, FileMode.Open, FileAccess.Read);
            WebClient theWebClient = new WebClient();
            string GMTime = DateTime.Now.ToUniversalTime().ToString("r");
            MD5CryptoServiceProvider theMD5Hash = new MD5CryptoServiceProvider();
            byte[] hashDatas;
            hashDatas = theMD5Hash.ComputeHash(new byte[( int )theFileStream.Length]);
            string contentMD5 = Convert.ToBase64String(hashDatas);
            // HMACSHA1 theHMACSHA1 = new HMACSHA1();
            KeyedHashAlgorithm theHMACSHA1 = KeyedHashAlgorithm.Create("HmacSHA1");
            //  KeyedHashAlgorithm theHMACSHA1 = KeyedHashAlgorithm.Create("1".ToUpperInvariant());
            theHMACSHA1.Key = Encoding.UTF8.GetBytes("AWXbSJ07yjX0f278Hgarw2f3Z6Q=".ToCharArray());
            string headerStr = "PUT\n"   contentMD5   "\n"   contentType   "\n"
                 GMTime   "\n"   bucket   "/"   fileName;
            byte[] rstRes = theHMACSHA1.ComputeHash(Encoding.UTF8.GetBytes(headerStr.ToCharArray()));
            string strSig = Convert.ToBase64String(rstRes);
            theWebClient.Headers.Add(HttpRequestHeader.Authorization, "OSS ia1lncawwinvh2vu2xjkvmdg:"   strSig);
            theWebClient.Headers.Add(HttpRequestHeader.ContentMd5, contentMD5);
            theWebClient.Headers.Add(HttpRequestHeader.ContentType, contentType);
            theWebClient.Headers.Add("X-OSS-Date", GMTime);
            try
            {
                byte[] ret = theWebClient.UploadFile(" http冒号//storage.aliyun.com/"   bucket   "/"   fileName, "PUT", filePath);      
          string strMessage = Encoding.ASCII.GetString(ret);
                return strMessage;
            }
            catch (WebException e)
            {
                Stream stream = e.Response.GetResponseStream();
                StreamReader reader = new StreamReader(stream);
                return reader.ReadToEnd();
            }
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