delphi+MySQL的AdoDataset指针不对

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。

QueryDataset.Next();这里报错：什么错误信息，表是否有主键 
 
CursorType := ctDynamic
试试