I recently ran into an issue where I was trying to dynamically create a Panel with Buttons, Labels, ect and have it popup using the AJAX PopupControlExtender.  The problem was that whenever you would click on the Button, it wouldn't fire the click event.  The event was there, it just wouldn't execute.  Anyway, to make a long story short.. I had to change the Button's UseSubmitBehaviour to false to get it working.

i.e ( Button1.UseSubmitBehavior = false);

Hopefully, someone will find this post and save themselves some time.

The following code can be used for creating a spreadsheet on the fly and presenting it to a user for download.  It's important to note that it doesn't really create a spreadsheet on the fly... rather it copies a template sheet and then populates the copy.  Either way, to the user its transparent.  Just create a template sheet with all of your column names and store it in one of your project folders.

The code is as follows:

protected void btn_exportdata_Click(object sender, EventArgs e)

     {               
         //Creates a guid named filequid (unique identifier)
        Guid fileguid = Guid.NewGuid();
        //String the new filename  * Replace “Server_Name” & “Folder_Name”     
        string filename = @"\\Server_Name\Folder_Name\" + fileguid.ToString() + ".csv";
        
        //Create the new file and copy the template column names into it * Replace “Server_Name” & “Folder_Name”
       File.Copy(@"\\Server_Name\Folder_Name\Template.xls", filename);              
      
       //Make your database connection
        string cs = ConfigurationManager.ConnectionStrings["ConnectionString"].ToString();
        SqlConnection dbConnection = new SqlConnection(cs);
        dbConnection.Open();
       
       //Create sql command
        SqlCommand export_data = dbConnection.CreateCommand();
       
       //Populate sql command * Replace “Select * from customers” with your select command
       export_data.CommandText = @"insert into OPENROWSET('Microsoft.Jet.OLEDB.4.0', 'Excel 8.0;Database=" +     filename + ";', 'SELECT * FROM [Sheet1$]') select * from customers";
                    
        //Execute sql command
         export_data.ExecuteNonQuery();
       
        //Close the connection
         dbConnection.Close();
       
      //Present the spreadsheet to the user for download * Replace “sitename.com/Folder_Name” with your specifics
        Response.Redirect("http://sitename.com/Folder_Name/" + fileguid.ToString() + ".csv");
    }