多线程查询数据库，偶尔会丢掉一个线程。但大部分时候是正常。苦恼中。该怎么处理

多线程查询数据库，偶尔会丢掉一个线程。但大部分时候是正常。苦恼中。
如题。使用多个线程查询数据，然后汇总为1个数据集。偶尔会丢掉一个线程查询的数据集。

可能是什么原因呢。
代码很长，熟悉多线程的兄弟提示下，我贴相关的代码出来。
丢掉线程后，下次查询会出来如下错误。
'Access violation at address 770F4C27 in module 'oleaut32.dll'
没有丢掉线程时，无此错误提示。

一共就5个线程而已。
确实是很奇怪的问题。
我已经仔细检查了数据集，在少数情况（大概十几次中出现1次）
有1个线程的数据集丢失。所有代码如下
=====线程的代码==================
unit QueryThread;
interface
   
uses  
  Classes, Messages, Provider, ADODB, ActiveX;

const
  WM_QueryDone = WM_User+1010;

type
  TTag = 0..4;
  TQueryThread = class(TThread)
  private
  FTag: TTag;
  FHandle: THandle;
  FQuery: TADOQuery;
  function CreateSQL(const Tag: TTag): string;
  protected
  procedure Execute; override;
  public
  constructor Create(const ADataSetProvider: TDataSetProvider; ATag: TTag; AHandle: THandle);
  end;
   
implementation

uses  
  Windows, Forms, SysUtils;  
   
{ TQueryThread }  

constructor TQueryThread.Create(const ADataSetProvider: TDataSetProvider;
  ATag: TTag; AHandle: THandle);  
begin
  FTag := ATag;
  FHandle := AHandle;
  FQuery := TADOQuery.Create(nil);
  FQuery.ConnectionString := ' Provider=SQLOLEDB.1;Password=111;Persist Security Info=True;User ID=sa;Initial Catalog=test'; //写入链接串
  FQuery.SQL.Text := CreateSQL(FTag); //创建SQL语句
  ADataSetProvider.DataSet := FQuery;
  FreeOnTerminate := True;  
  inherited Create(False);
end;

function TQueryThread.CreateSQL(const Tag: TTag): string;
begin
  case Tag of
  0: Result := 'select top 5 * from VW_test where rq= ''2009-02-26 00:00:00.000''';  
  1: Result := 'select top 5 * from VW_test where rq= ''2009-02-27 00:00:00.000''';  
  2: Result := 'select top 5 * from VW_test where rq= ''2009-02-28 00:00:00.000''';  
  3: Result := 'select top 5 * from VW_test where rq= ''2009-03-01 00:00:00.000''';  
  4: Result := 'select top 5 * from VW_test where rq= ''2009-03-02 00:00:00.000''';  
  end;
end;

procedure TQueryThread.Execute;
begin
  CoInitialize(nil);
  try
  FQuery.Open;
  PostMessage(FHandle, WM_QueryDone, FTag, 0); //发送查询结束消息
  finally
  CoUnInitialize;
  end;
end;
end.

=======================

====调试的代码==
unit Unit1;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls, Buttons, DB, DBClient, Grids, DBGrids, Provider,
  QueryThread,ADODB,Contnrs;

type
  TMainForm = class(TForm)
  BRefresh: TBitBtn;
  CDSLocal: TClientDataSet;
  CDSRemote_2: TClientDataSet;
  CDSRemote_1: TClientDataSet;
  CDSRemote_3: TClientDataSet;
  CDSRemote_4: TClientDataSet;
  DSPLocal: TDataSetProvider;
  DSPRemote_1: TDataSetProvider;
  DSPRemote_2: TDataSetProvider;
  DSPRemote_3: TDataSetProvider;
  DSPRemote_4: TDataSetProvider;
  DSLocal: TDataSource;
  DBGridLocal: TDBGrid;
  ADOConnection1: TADOConnection;
  BtnOneThread: TBitBtn;
  DS_OneThread: TDataSource;
  CDS_OneThread: TClientDataSet;