SQL2005的维护计划无法删除的解决方法

今天开发中，发现维护计划无法删除删除了，遂发现下面的代码，希望对碰到类似问题的朋友有所帮助。

select * from sysmaintplan_plans
select * from sysmaintplan_log
select * from sysmaintplan_subplans

2.根据ID号删除相应的"维护计划"
代码如下:
delete from sysmaintplan_log where plan_id = ' ‘
delete from sysmaintplan_subplans where subplan_id = ' '
delete from sysmaintplan_plans where id = ' '