why this is happening?

protected void Upload(object sender, System.EventArgs e)
{
//Upload and save the file
string excelPath = Server.MapPath("~/Files/") + Path.GetFileName(FileUpload1.PostedFile.FileName);
string DuplicateEtry = "These Records are Already Present..!";
FileUpload1.SaveAs(excelPath);

string conString = string.Empty;
string extension = Path.GetExtension(FileUpload1.PostedFile.FileName);
//select virsion of Excel 2007 0r 2010
switch (extension)
{
case ".xls": //Excel 97-03
conString = ConfigurationManager.ConnectionStrings["Excel03ConString"].ConnectionString;
break;
case ".xlsx": //Excel 07 or higher
conString = ConfigurationManager.ConnectionStrings["Excel07+ConString"].ConnectionString;
break;
}
conString = string.Format(conString, excelPath);

try
{
using (OleDbConnection excel_con = new OleDbConnection(conString))
{
excel_con.Open();
string sheet1 = excel_con.GetOleDbSchemaTable(OleDbSchemaGuid.Tables, null).Rows[0]["TABLE_NAME"].ToString();
DataTable dtExcelData = new DataTable();

//[OPTIONAL]: It is recommended as otherwise the data will be considered as String by default.
dtExcelData.Columns.AddRange(new DataColumn[19] { new DataColumn("NGOName", typeof(string)),
new DataColumn("RegiID", typeof(int)),
new DataColumn("ExName", typeof(string)),
new DataColumn("Designation", typeof(string)),
new DataColumn("Skill", typeof(string)),
new DataColumn("Membership", typeof(string)),
new DataColumn("Address ", typeof(string)),
new DataColumn("City ", typeof(string)),
new DataColumn("Pin ", typeof(int)),
new DataColumn("District ", typeof(string)),
new DataColumn("State ", typeof(string)),
new DataColumn("Country ", typeof(string)),
new DataColumn("Landline ", typeof(int)),
new DataColumn("Con1", typeof(string)),
new DataColumn("Con2 ", typeof(string)),
new DataColumn("Email1 ", typeof(string)),
new DataColumn("Email2 ", typeof(string)),
new DataColumn("Website ", typeof(string)),
new DataColumn("Description", typeof(string)),
});
using (OleDbDataAdapter oda = new OleDbDataAdapter("SELECT * FROM [" + sheet1 + "]", excel_con))
{
oda.Fill(dtExcelData);
}
excel_con.Close();

string consString = ConfigurationManager.ConnectionStrings["CS2"].ConnectionString;
using (SqlConnection con = new SqlConnection(consString))
{
using (SqlBulkCopy sqlBulkCopy = new SqlBulkCopy(con))
{
//Set the database table name
sqlBulkCopy.DestinationTableName = "dbo.ORG_Tb";

//[OPTIONAL]: Map the Excel columns with that of the database table
sqlBulkCopy.ColumnMappings.Add("NGOName", "NGOName");
sqlBulkCopy.ColumnMappings.Add("RegiID", "RegiID");
sqlBulkCopy.ColumnMappings.Add("ExName", "ExName");
sqlBulkCopy.ColumnMappings.Add("Designation", "Designation");
sqlBulkCopy.ColumnMappings.Add("Skill", "Skill");
sqlBulkCopy.ColumnMappings.Add("Membership", "Membership");
sqlBulkCopy.ColumnMappings.Add("Address", "Address");
sqlBulkCopy.ColumnMappings.Add("City", "City");
sqlBulkCopy.ColumnMappings.Add("Pin