MWS fba api bad request c#

Question

hi i am testing MarketplaceWebService.Samples.But it responses alway bad request. invaild request. can anyone help to take a look. thanks.

SubmitFeedRequest request = new SubmitFeedRequest();
            request.Merchant = merchantId;
            request.MWSAuthToken = "<Your MWS Auth Token>"; // Optional
            request.MarketplaceIdList = new IdList();
            request.MarketplaceIdList.Id = new List<string>(new string[] { marketplaceId });



            request.FeedContent = File.Open("feed.xml", FileMode.Open, FileAccess.Read);


            request.ContentMD5 = MarketplaceWebServiceClient.CalculateContentMD5(request.FeedContent);
            request.FeedContent.Position = 0;

            request.FeedType = "_POST_PRODUCT_DATA_";

            SubmitFeedSample.InvokeSubmitFeed(service, request);

feed.xml 1.01 machantid Product false 1 Update testsku UPC 123456789