Error: 500 on ajax call on webmethod.

Hi Expert,

Can anyone tell me on why this error pop up.

Please see below code

Code Behide

<WebMethod()> _
    Public Sub SearchByNames(ByVal Name As String, ByVal Location As String)
        Try
            con.Open()
            Dim cmd As SqlCommand = con.CreateCommand
            cmd.CommandText = "usp_GetSearchName"
            cmd.CommandType = CommandType.StoredProcedure
            cmd.Parameters.AddWithValue("@Name", Name)
            cmd.Parameters.AddWithValue("@BranchCode", Location)
            Dim dr As SqlDataReader = cmd.ExecuteReader
            Dim dt As New DataTable
            dt.Load(dr)
            If dt.Rows.Count > 0 Then
                GridView3.DataSource = dt
                GridView3.DataBind()
            Else
                GridView3.DataSource = Get_EmptyDataTableSearchbyName()
                GridView3.DataBind()
            End If
            cmd.ExecuteNonQuery()
        Catch ex As Exception
            Session("error_message") = ex.Message & "</br>" & "Please check the Grid Search by Name."
        Finally
            If con IsNot Nothing Then
                con.Close()
                con.Dispose()
            End If
        End Try
    End Sub

Ajax call

        function SearchByName() {
            var checkboxSearchName = document.getElementById("<%=ChkSearchbyName.ClientID%>").checked;
            var SearchName = document.getElementById("<%=txtSearchBarcode.ClientID%>").value;
            var Location = "1";

            if (checkboxSearchName === true) {
                var parameter = { Name: SearchName, Location: Location };
                $.ajax({
                    type: "POST",
                    url: "GCPGCISPage.aspx/SearchByNames",
                    contentType: "application/json; charset=utf-8",
                    data: JSON.stringify(parameter),
                    success: function (r) {$find("mpe").show();
                        return false;
                    },
                    error: function (result) {
                        alert("Error " + result.status);
                    }
                });
            }
        }

Thanks and advance..