Work Issues

As mentioned by other users you can use any language of your choice.
But keep in mind that ERPs are very complex system which you cannot build over one night. It takes long time. So it will be beneficial if you can leverage the built in features of some framework. Becuse the framework take care of most of the things. It separates the user, business logic and database. From that perspective Java (J2EE) is a good choice. I use Oracle ADF to build ERP along with PL SQL and JavaScript.

$(document).ready(function () {
    var select = $("#<%=lblMultiSelect.ClientID%>");
    var senddata = select.val();
    var txt = $("#<%=listBoxValue.ClientID%>"); //<<just putting id to a textbox here for testing purposes

    select.change(function (e) {
        $.ajax({
            type: "POST",
            url: "CS.aspx/GetCurrentTime",
            data: '{name: "' + senddata + '" }',
            contentType: "application/json; charset=utf-8",
            dataType: "json",
            success: OnSuccess,
            failure: function(response) {
                alert(response.d);
            }
        });
    });
});

function OnSuccess(response) {
    $.each(response, function (i, el) {

        // your code for listbox

    });
}