Ｃ＃　浏览器直接上传

最近需要用到浏览器端到ＯＳＳ服务器的直接上传下载功能。用C#做了个demo，代码如下：            　　　try
            {
                ObjectMetadata metadata = new ObjectMetadata();
                // 可以设定自定义的metadata。
                metadata.UserMetadata.Add("myfield", "test");


                OssClient ossClient = new OssClient(new Uri("http://oss-cn-qingdao.aliyuncs.com/"), accessId, accessKey); // 青岛数据中心  


                //OssClient ossClient = new OssClient(accessId, accessKey); // 杭州数据中心  
                //*
                //<-----------------------------URL Start--------------------------------
                AccessControlList accs = ossClient.GetBucketAcl(bucketName);


                string imgurl = string.Empty;


                SignHttpMethod method = new SignHttpMethod();
                if(methodType == 0) // 根据传入参数判断生成胡 uri类型
                    method = SignHttpMethod.Get;
                else
                    method = SignHttpMethod.Put;
                //if (!accs.Grants.Any())
                {
                    GeneratePresignedUriRequest request = new GeneratePresignedUriRequest(bucketName, key, method);
                    
                    int time = 0;
                    int.TryParse(delaytime, out time);
                    request.Expiration = DateTime.Now.AddSeconds(time); // 有效时间 ，单位 秒


                    imgurl = ossClient.GeneratePresignedUri(request).AbsoluteUri;


                    MessageBox.Show("方法为：" method " 有效时间为（秒）：=" time);
                }
                // else
                {
                    // imgurl = string.Format("http://{0}.oss.aliyuncs.com/{1}", bucketName, key);
                }


                //context.Response.Write(String.Format("{0}|{1}|{2}|{3}", imgurl, imgurl, imgurl, key));
                //------------------------------URL END---------------------------------->
                //*/
                return imgurl.ToString();
            }
            catch (AggregateException ex)
            {
                throw ex;
            }
下载功能都正常，但是上传得时候老是返回

<Error>

<Code>SignatureDoesNotMatch</Code>
<Message>The request signature we calculated does not match the signature you provided. Check your key and signing method.</Message>
<StringToSignBytes>47 45 54 0A 0A 0A 31 33 39 33 32 30 35 33 38 35 0A 2F 73 69 75 69 62 75 63 6B 65 74 31 2F 31 32 33 2E 74 78 74</StringToSignBytes>
<SignatureProvided>aN3L9ODePhNqQoIHrrtThVEaHUo=</SignatureProvided>
<StringToSign>GET 1393205385 /siuibucket1/123.txt</StringToSign>
<OSSAccessKeyId>QAWi14lIVk1DI3pp</OSSAccessKeyId>
<RequestId>530AA056236AAA280251D094</RequestId>
<HostId>siuibucket1.oss-cn-qingdao.aliyuncs.com</HostId>
</Error>
求解释？从代码能看到，上传下载都是用了同一个流程来签名，SignatureDoesNotMatch怎么会单单上传出现这个问题？
注：由于没有指定上传文件本地路径，我的上传文件和我的exe放在一个目录