Calling ASMX from jQuery

One thing that stands out is you have UseHttpGet=true but in your jQuery code you are using POST.

Also here is a test page I created calling an ASMX page.

[WebMethod]
public Catalog[] GetCatalog()
{
    Catalog[] catalog = new Catalog[1];
    Catalog cat = new Catalog();
    cat.Author = "Jim";
    cat.BookName ="His Book";
    catalog.SetValue(cat, 0);
    return catalog;
}

<script type="text/javascript">
    $(document).ready(function() {
    $.ajax({
            type: "POST",
            url: "default.asmx/GetCatalog",
            cache: false,
            contentType: "application/json; charset=utf-8",
            data: "{}",
            dataType: "json",
            success: handleHtml,
            error: ajaxFailed
        });
    });

    function handleHtml(data, status) {
        for (var count in data.d) {
            alert(data.d[count].Author);
            alert(data.d[count].BookName);
        }
    }

    function ajaxFailed(xmlRequest) {
        alert(xmlRequest.status + ' \n\r ' + 
              xmlRequest.statusText + '\n\r' + 
              xmlRequest.responseText);
    }
</script>