Please help to check when loading, error persists below code

Question

Please help to check when loading, error persists below code :-

 

1) Default.aspx

<script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.6.2/jquery.min.js"></script>
<script type="text/javascript">
$(document).ready(function () {
$.ajax({
type: "POST",
contentType: "application/json; charset=utf-8",
url: "Default.aspx/BindDatatable",
data: "{}",
dataType: "json",
success: function (data) {
for (var i = 0; i < data.d.length; i++) {
$("#gvDetails").append("<tr><td>" + data.d[i].UserId + "</td><td>" + data.d[i].UserName + "</td><td>" + data.d[i].Location + "</td></tr>");
}
},
error: function (result) {
alert("Error");
}
});
});
</script>
<style type="text/css">
table,th,td
{
border:1px solid black;
border-collapse:collapse;
}
</style>
<form id="form1" runat="server">
<asp:GridView ID="gvDetails" runat="server">
<HeaderStyle BackColor="#DC5807" Font-Bold="true" ForeColor="White" />
</asp:GridView>
</form>

2) Default.aspx code behind

protected void Page_Load(object sender, EventArgs e)
{
if (!IsPostBack)
{
BindColumnToGridview();
}
}
private void BindColumnToGridview()
{
DataTable dt = new DataTable();
dt.Columns.Add("UserId");
dt.Columns.Add("UserName");
dt.Rows.Add();
gvDetails.DataSource = dt;
gvDetails.DataBind();
gvDetails.Rows[0].Visible = false;
}
[System.Web.Services.WebMethod]
public static UserDetails[] BindDatatable()
{
DataTable dt = new DataTable();
List<UserDetails> details = new List<UserDetails>();
using (OracleConnection con = new OracleConnection("Data Source=(DESCRIPTION ="
+ "(ADDRESS_LIST=(ADDRESS=(PROTOCOL=TCP)(HOST=xxx.xxx.xxx.xxx)(PORT=xxxx)))"
+ "(CONNECT_DATA=(SERVER=DEDICATED)(SERVICE_NAME=xxxxxx)));"
+ "User Id=xxxx;Password=xxxxxxxx;"))
{
using (OracleCommand cmd = new OracleCommand("SELECT UserId,UserName FROM table", con))
{
con.Open();
OracleDataAdapter da = new OracleDataAdapter(cmd);
da.Fill(dt);
foreach (DataRow dtrow in dt.Rows)
{
UserDetails user = new UserDetails();
user.UserId = dtrow["UserId"].ToString();
user.UserName = dtrow["UserName"].ToString();
details.Add(user);
}
}
}
return details.ToArray();
}
public class UserDetails
{
public string UserId { get; set; }
public string UserName { get; set; }
}