Pop-up message error

 

protected void downloadPDFBtn_Click(object sender, ImageClickEventArgs 
e)
    {
        //calls 
the method to create the datatable
        
GetCustomMadeDataTable();
        //calls 
the method to generate the pdf from the 
datatable
        GeneratePDF(table);

        //popup error message when staff 
choose one of the field under the Reminder field and click on the "download PDF" 
button.
        if 
(DropDownList1.SelectedItem.Value != 
null)
        
{            

            
MessageBox.Show("There is no timetable available 
for");
            
Response.Redirect("DownloadTimetable.aspx");                    

        }