contentType: "application/x-www-form-urlencoded; charset=utf-8",

...
var data = {};
data[element.name] = value;
$.ajax($.extend(true, {
url: param,
mode: "abort",
port: "validate" + element.name,
dataType: "json",
data: data,
....

remote: {
url: "ajax.aspx?a=xxx",
type: "post",
dataType: "json",
contentType: "application/x-www-form-urlencoded; charset=utf-8",
data: { txt1: function() { return $("#txt1").val(); } }
}