I post data to my aspx file qith the following code:
 $.ajax({
            type: \'POST\',
            url: \"Ajax_Text.aspx?rand=\" + myRand
                            
        POST data are not send in query string but added to the request body. Try this code:
$.ajax({
        type: 'POST',
        url: "Ajax_Text.aspx",
        data: {'rand': myRand, 'id': $(".articleID").attr('title'), 'text': $("#text").val()},
        cache: false,
        beforeSend: function () {
        },
        success: function (data) {
            alert(data); 
        }
    });
You are "posting" the data (text) as a query string (as part of URL) so you have to use Request.QueryString.