I'm using a simple example from Amazon documentation for ItemSearch and I get a strange error: "The remote server returned an unexpected response: (400) Bad Request."

This is the code:

public static void Main()
        {
            //Remember to create an instance of the amazon service, including you Access ID. 

            AWSECommerceServicePortTypeClient service = new AWSECommerceServicePortTypeClient(new BasicHttpBinding(),
                                                                                              new EndpointAddress(
                                                                                                "http://webservices.amazon.com/onca/soap?Service=AWSECommerceService"));


            AWSECommerceServicePortTypeClient client = new AWSECommerceServicePortTypeClient(
             new BasicHttpBinding(),
             new EndpointAddress("http://webservices.amazon.com/onca/soap?Service=AWSECommerceService"));

            // prepare an ItemSearch request  
            ItemSearchRequest request = new ItemSearchRequest();
            request.SearchIndex = "Books";
            request.Title = "Harry+Potter";
            request.ResponseGroup = new string[] { "Small" };
            ItemSearch itemSearch = new ItemSearch();
            itemSearch.Request = new ItemSearchRequest[] { request };
            itemSearch.AWSAccessKeyId = accessKeyId;

            // issue the ItemSearch request
            try
            {
                ItemSearchResponse response = client.ItemSearch(itemSearch);
                // write out the results  

                foreach (var item in response.Items[0].Item)
                {
                    Console.WriteLine(item.ItemAttributes.Title);
                }
            }
            catch(Exception e)
            {
                Console.ForegroundColor = ConsoleColor.Red;
                Console.WriteLine(e.Message);
                Console.ForegroundColor = ConsoleColor.White;
                Console.WriteLine("Press any key to quit...");
                Clipboard.SetText(e.Message);
            }
            Console.ReadKey();

What is wrong?