Syntax error in Insert into statement

Hi, here is my code.

String sConnectionString = "Provider=Microsoft.Ace.OLEDB.12.0;Data Source=" + excelfile + ";Extended Properties=Excel 12.0;";
                OleDbConnection olecon = new OleDbConnection(sConnectionString);
                olecon.Open();
                //string stdemo;
                string olestr;
                olestr = "Insert Into  [Sheet1$] (Buyer,Salutation,Company,AddressLine1,City,State,Zip,date) Values (?,?,?,?,?,?,?,?)";
               // OleDbCommand olecmd;

                using (OleDbConnection conn = new OleDbConnection(sConnectionString))
                {
                    for (int i = 0; i < dttmp.Rows.Count; i++)
                    {
                        using (OleDbCommand cmd1 = new OleDbCommand(olestr, conn))
                        {
                            cmd1.Parameters.Clear();
                            cmd1.CommandType = CommandType.Text;
                            cmd1.Parameters.AddWithValue("Buyer", dttmp.Rows[i]["Buyer"]);
                            cmd1.Parameters.AddWithValue("Salutation", dttmp.Rows[i]["Salutation"]);
                            cmd1.Parameters.AddWithValue("Company", dttmp.Rows[i]["Company"]);
                            cmd1.Parameters.AddWithValue("AddressLine1", dttmp.Rows[i]["AddressLine1"]);
                            cmd1.Parameters.AddWithValue("City", dttmp.Rows[i]["City"]);
                            cmd1.Parameters.AddWithValue("State", dttmp.Rows[i]["State"]);
                            cmd1.Parameters.AddWithValue("Zip", dttmp.Rows[i]["Zip"]);
                            cmd1.Parameters.AddWithValue("date", dttmp.Rows[i]["date"]);
                            conn.Open();
                            cmd1.ExecuteNonQuery();
                        }
                    }
                }

While excute the cmd1 i got the Error like : Syntax error in Insert into statement

Can anyone please give me the solutions.

Thanks in Advance.