I'm struggling with the final part of getting my first bit of code working with the AWS - I have got this far, I attached the web reference in VS and this have this

        amazon.AWSECommerceService service = new amazon.AWSECommerceService();

        // prepare an ItemSearch request
        amazon.ItemSearchRequest request = new amazon.ItemSearchRequest();
        request.SearchIndex = "DVD";
        request.Title = "scream";
        request.ResponseGroup = new string[] { "Small" };

        amazon.ItemSearch itemSearch = new amazon.ItemSearch();
        itemSearch.AssociateTag = "";
        itemSearch.Request = new ItemSearchRequest[] { request };
        itemSearch.AWSAccessKeyId = ConfigurationManager.AppSettings["AwsAccessKeyId"];

        itemSearch.Request = new ItemSearchRequest[] { request };
        ItemSearchResponse response = service.ItemSearch(itemSearch);

        // write out the results
        foreach (var item in response.Items[0].Item)
        {
            Response.Write(item.ItemAttributes.Title + "<br>");
        }

I get the error

The request must contain the parameter Signature.

I know you have to 'sign' requests now, but can't figure out 'where' I would do this or how? any help greatly appreciated?