ExcelApp3.ActiveWorkbook.SaveCopyAs("C:\\Users\\RAJENDRAN\\Desktop\\clientstatement"+DateTime.Now.ToShortDateString()+".xls");
ExcelApp3.ActiveWorkbook.Saved = true;
use the below istead of that :
Response.ClearContent();
Response.Buffer = true;
Response.AddHeader("content-disposition", string.Format("attachment; filename={0}", "clientstatement"+DateTime.Now.ToShortDateString()+".xls"));
Response.ContentType = "application/ms-excel";
StringWriter sw = new StringWriter();
HtmlTextWriter htw = new HtmlTextWriter(sw);
GridView1.AllowPaging = false;
btnview_Click(this, null);
GridView1.DataBind();
GridView1.RenderControl(htw);
Response.Write(sw.ToString());
Response.End();