这段连接数据库的代码为什么运行时出错（编译能通过，运行时出错）

这段连接数据库的代码为什么运行时出错，说什么访问被挂起，被隔离（编译能通过，运行时出错）
（1）DataModule
unit dbconn;interfaceuses
  SysUtils, Classes, DB, ADODB;type
  TdataModDBConn = class(TDataModule)
    connMain: TADOConnection;
    procedure DataModuleCreate(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;var
  dataModDBConn: TdataModDBConn;implementation{$R *.dfm}procedure TdataModDBConn.DataModuleCreate(Sender: TObject);
var connString:String;
begin
    connString:='Provider=Microsoft.Jet.OLEDB.4.0;Data Source=D:\abc.mdb;Persist Security Info=False';
    connMain.ConnectionString:=connString;
    connMain.Connected:=true;
end;end.
(2)主窗体
unit main;interfaceuses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, ExtCtrls, StdCtrls, jpeg, ComCtrls, DB, ADODB, dbconn;type
  TfrmMain = class(TForm)
    pnlTop: TPanel;
    pnlLeft: TPanel;
    splMain: TSplitter;
    pnlRight: TPanel;
    imgBanner: TImage;
    scrboxLeftMenu: TScrollBox;
    treeVLeftMenu: TTreeView;
    dataSetLeftMenu: TADODataSet;
    procedure FormClose(Sender: TObject; var Action: TCloseAction);
    procedure FormCreate(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;var
  frmMain: TfrmMain;implementation{$R *.dfm}procedure TfrmMain.FormClose(Sender: TObject; var Action: TCloseAction);
begin
    frmMain.Free;
    frmMain:=nil;
    Application.Terminate;
end;procedure TfrmMain.FormCreate(Sender: TObject);
var leftMenuRootNode:TTreeNode;
var name:String;
begin
        dataSetLeftMenu.Connection:=dataModDBConn.connMain;//好像执行到这一句出错
        dataSetLeftMenu.CommandText:='select * from menu';
        dataSetLeftMenu.Active:=true;        leftMenuRootNode:=treeVLeftMenu.Items.Add(nil,'菜单');
        while not dataSetLeftMenu.Eof do
        begin
            name:=dataSetLeftMenu.FieldValues['name'];
            treeVLeftMenu.Items.AddChild(leftMenuRootNode,name);
            dataSetLeftMenu.Next;
        end;end;end.