Web page "frozen" after export to Excel

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I have a gridview that I successfully export to Excel, however, after I close the excel file or save it, and return to the web page/ main page, all the controls are frozen and I have to refresh the page to get anything working. How can I correct that? pls. help me in this..

here's my code:

            //Get the data from database into datatable

            string strQuery = "select EMP_NAME, DEPT, SALARY, EMAIL_ID from EMPLOYEE";
            SqlCommand cmd = new SqlCommand(strQuery);
            DataTable dt = GetData(cmd);

            //Create a dummy GridView

            GridView GridView1 = new GridView();
            GridView1.AllowPaging = false;
            GridView1.DataSource = dt;
            GridView1.DataBind();

            HttpContext.Current.Response.Clear();
            HttpContext.Current.Response.Buffer = true;
            HttpContext.Current.Response.AddHeader("content-disposition", "attachment;filename=Excel.xls");
            HttpContext.Current.Response.Charset = "";
            HttpContext.Current.Response.ContentType = "application/vnd.ms-excel";
            StringWriter sw = new StringWriter();
            HtmlTextWriter hw = new HtmlTextWriter(sw);

            //Change the Header Row back to white color

            GridView1.HeaderRow.Style.Add("background-color", "#FFFFFF");

            //Applying stlye to gridview header cells

            for (int i = 0; i < GridView1.HeaderRow.Cells.Count; i++)
            {
                GridView1.HeaderRow.Cells[i].Style.Add("background-color", "#0F5E8E");

            }

            GridView1.RenderControl(hw);

            //style to format numbers to string

            string style = @"<style> .textmode { mso-number-format:\@; } </style>";
            HttpContext.Current.Response.Write(style);
            HttpContext.Current.Response.Output.Write(sw.ToString());
            HttpContext.Current.Response.Flush();
            HttpContext.Current.Response.End();

Thanks in advance,