delphi+MySQL问题

主要代码：

QueryDataset := TADODataSet.Create(nil);

with QueryDataset do

begin

    Active := False;

    AutoCalcFields := True;

    CommandType := cmdText;

    CommandTimeout := 30;

    CacheSize := 1;

    AutoCalcFields := True;

    CursorLocation := clUseClient;

    CursorType := ctKeyset;

    EnableBCD := True;

    Filtered := False;

    Prepared := False;

    LockType := ltOptimistic;

    MarshalOptions := moMarshalAll;

    StoreDefs := False;

    Tag := 0;

    connectionstring := '';

    try

      Connection := Conn;

    except

      on e:Exception do begin

        Result := False;

      end;

  CommandText := 'Select * from table order by idx';    

end;

while not QueryDataset.Eof do

begin

  Inc(NumberOfQueryResult);

  QueryDataset.Next();

end;

Freeandnil(QueryDataset);

如果table不做insert操作，没有问题，但如果insert 几条数据到table里面，
然后再运行以上程序，QueryDataset.Next();这里报错，好像AdoDataset指针不对了

MySQL版本：
mysql> select @@version;
+---------------------+
| @@version |
+---------------------+
| 5.0.81-community-nt |
+---------------------+
1 row in set (0.00 sec)

没见过的毛病，维护老产品用的delphi6.0开发。