能打开Excel2003文件，但是打开Excel2007文件失败，连接字符串没有有关问题

        private void MenuItem_Click(object sender, RoutedEventArgs e)//菜单点击事件        {            MenuItem mn=sender as MenuItem;            string openExcelFilename="";            string connectionString = "";            switch(mn.Header.ToString())//比较选取的菜单标题            {                case "Excel97-2003文件"://如果是"Excel97-2003文件"                    OpenFileDialog fileOpenExcel03 = new OpenFileDialog();\\执行打开文件对话框                    fileOpenExcel03.Filter = "Excel文件97-2003(*.xls)|*.xls";                    if (fileOpenExcel03.ShowDialog() != true)                        return;                    openExcelFilename = fileOpenExcel03.FileName.Trim();                    dbFilenameExcel = fileOpenExcel03.SafeFileName;                    connectionString = @"Provider=Microsoft.Jet.OLEDB.4.0;Data Source="+openExcelFilename + ";Extended Properties='Excel 8.0'";\\根据打开的文件生成连接字符串                    break;                case "Excel2007-10文件"://如果是"Excel2007-10文件"                    OpenFileDialog fileOpenExcel07 = new OpenFileDialog();\\执行打开文件对话框                    fileOpenExcel07.Filter = "Excel2007-10文件(*.xlsx)|*.xlsx";                    if (fileOpenExcel07.ShowDialog() != true)                        return;                    openExcelFilename = fileOpenExcel07.FileName.Trim();                    dbFilenameExcel = fileOpenExcel07.SafeFileName;                    connectionString =@"Provider=Microsoft.ACE.OLEDB.12.0;Data Source="+openExcelFilename + ";Extended Properties='Excel 12.0'";\\根据打开的文件生成连接字符串                    break;               }            OleDbConnection ODCExcel = new OleDbConnection(connectionString);//创建连接            SelectWindow selectWin = new SelectWindow();//构造了一个新窗体            List<string> tableNames = GetTableNames(ODCExcel);//这句话用来获取Excel文件的表名            if (tableNames.Count <= 0)                return;            selectWin.cmbTableList.Items.Clear();//清空新窗体上名为cmbTableList的ComboBox的内容            selectWin.cmbTableList.ItemsSource = tableNames;//把获取的表名加入到ComboBox中            if (selectWin.ShowDialog() != true)                return;            tableNameExcel = "[" + selectWin.cmbTableList.Text + "]";            DataSet dsExcel=new DataSet();            string selectString = "select * From " + tableNameExcel;            OleDbDataAdapter ODCAExcel = new OleDbDataAdapter(selectString, ODCExcel);            try            {                ODCAExcel.Fill(dsExcel, "tableOpening");            }            catch (Exception ex)            {                MessageBox.Show(ex.Message);            }        }        private List<string> GetTableNames(System.Data.Common.DbConnection dbConnection)        {            List<string> tableNames = new List<string>();            try            {                dbConnection.Open();                System.Data.DataTable schema = dbConnection.GetSchema("Tables");                foreach (System.Data.DataRow r in schema.Rows)                {                    tableNames.Add((string)r["Table_Name"]);                }            }            catch (Exception ex)            {                MessageBox.Show(ex.Message);            }            finally            {                dbConnection.Close();            }            return tableNames;        }