结构化存储问题，请帮忙看看。

//stgRoot全局变量
问题：在Button1Click中可以把数据流中的数据读上来，而在Button2Click
中却不能，这是什么问题呢？请帮忙看看，谢谢！
procedure TForm1.Button1Click(Sender: TObject);
type
  datared=record
  com:String;
  dd:Integer;
  end;
VAR
  indata:array of datared;
  outdata:array of datared;
  stmData,outDatas:IStream;
  os:tolestream;
  instr,outstr:string;
  bytewrite,byteread:longint;
begin
  TRY
  if StgOpenStorage('d:\structfile\structdemo.ss',nil,STGM_READWRITE or STGM_SHARE_EXCLUSIVE,
     NIL,0,stgRoot)=STG_E_FILENOTFOUND then
     olecheck(stgCreateDocFile('d:\structfile\structdemo.ss',STGM_CREATE OR STGM_READWRITE
       or STGM_SHARE_EXCLUSIVE ,0,stgRoot));  EXCEPT
  END;
  olecheck(stgRoot.CreateStream('computer',STGM_CREATE OR STGM_WRITE
    or STGM_SHARE_EXCLUSIVE,0,0,outDatas));
  setlength(indata,1);
  indata[0].com:='com1';
  indata[0].dd:=19600;
  outDatas.Write(@indata,sizeof(indata),@bytewrite);
  stgRoot:=nil;  StgOpenStorage('d:\structfile\structdemo.ss',nil,STGM_READWRITE or STGM_SHARE_EXCLUSIVE,
     NIL,0,stgRoot);  olecheck(stgRoot.OpenStream('computer',nil,STGM_READWRITE OR STGM_SHARE_EXCLUSIVE,0,stmData));
  setlength(outdata,1);
  stmData.read(@outdata,sizeof(outdata),@byteread);
//数据可以读出来
  //这是outdata[0].com:='COM1';
end;procedure TForm1.Button2Click(Sender: TObject);
type
  datared=record
  com:String;
  dd:Integer;
  end;
var
  stmData:IStream;
  outdata:array of datared;
  os:tolestream;
  byteread:integer;
begin
 StgOpenStorage('d:\structfile\structdemo.ss',nil,STGM_READWRITE or STGM_SHARE_EXCLUSIVE,
     NIL,0,stgRoot);  olecheck(stgRoot.OpenStream('computer',nil,STGM_READWRITE OR STGM_SHARE_EXCLUSIVE,0,stmData));
  setlength(outdata,1);
  stmData.read(@outdata,sizeof(outdata),@byteread);
//数据读不出来,为什么呢？
//  这时outdata[0].com:='';end;当我把数据写完后退出程序，再启动程序时执行Button2Click也不行。