用delphi往oracle中存取图片，取没问题但是存的时候总出错

procedure TForm1.Button2Click(Sender: TObject);
begin
  with wQuery1 do
    begin
      Close;
      SQL.Clear;
      SQL.Text:='select * from picture';
      Prepared;
      Open;
      Pstream1:=TMemoryStream.Create;
      PStream2:=TMemoryStream.Create;
      PStream2:=PStream;
      TBlobField(FieldByName('IMAGE')).SaveToStream(Pstream1);
      Pstream1.Position:=0;
      PBmp1:=TBitmap.Create;
      PBmp1.LoadFromStream(Pstream1);
      Image1.Picture.Bitmap.Assign(PBmp1);
    end;
end;     //以上是读取图片  没有问题
procedure TForm1.Button4Click(Sender: TObject);
begin
  if OpenDialog1.Execute then
    FileStr:=OpenDialog1.FileName
  else
    Exit;
  PBmp:=TBitmap.Create;
  PStream:=TMemoryStream.Create;
  PBmp.LoadFromFile(FileStr);
  PBmp.SaveToStream(PStream);
  with wQuery1 do
    begin
      Close;
      SQL.Clear;
      SQL.Text:='insert into picture (image) values (:image)';
      ParamByName('image').LoadFromStream(PStream,ftBlob);
      try
        ExecSQL;
        ShowMessage('OK');
      except
        ShowMessage('NO');
      end;
    end;
end;    //以上是存图片  总是出错  
  提示错误为unimplemented or unreasonable conversion requested  大家帮帮忙