Web Forms :: Export From Datagrid View To Excel File In Asp C#

i have someecords in grid i want ot export in excel file . i use code like below

protected void btnExportDB_Click(object sender, EventArgs e)
{
Response.Clear();
Response.Buffer = true;
Response.ContentType = "application/vnd.ms-excel";
Page.EnableViewState = false;
Response.Charset = "";
Response.AddHeader("Content-Disposition", "inline;filename=voucher.xls");
System.IO.StringWriter oStringWriter = new System.IO.StringWriter();
System.Web.UI.HtmlTextWriter oHtmlTextWriter = new System.Web.UI.HtmlTextWriter(oStringWriter);
grdMembers.RenderControl(oHtmlTextWriter);
Response.Write(oStringWriter.ToString());
Response.End();
}

on use this code on button click event.. file is generating but when i use same file for import in to database It gave me Error : External table is not in the expected format. For prob. of Format Type for Excel.