过程：触发器无效，重新验证失败

Question

我收到错误“触发器无效且重新验证失败”，因为我写的是从表中删除学生的过程。

程序dropstudent

 (v_sid in students.sid%type,
  v_classid in classes.classid%type,
  status1 out varchar,
  status2 out varchar,
  status3 out varchar) is
  c_sid students.sid%type;
  c_classid  enrollments.classid%type;
  cnt number;
  v_size classes.class_size%type;
  begin
  chk_sid_classid(v_sid,v_classid);

  select sid,classid into c_sid,c_classid
  from enrollments
  where sid = v_sid and classid = v_classid;
  select count(sid) into cnt
  from enrollments
 where sid = v_sid
 group by sid;
 if(cnt = 1) then
 status1:='This student is not enrolled in any classes.';
 else
 status1:=' ';
 end if;
select class_size into v_size
 from classes
 where classid = v_classid;
 if (v_size = 1) then
 status2:='The class now has no students.';
 else
 status2:=' ';
 end if;
 delete from enrollments where sid = v_sid and classid = v_classid;
 exception
 when no_data_found then
 status3 := 'The student is not enrolled in the class';

端;

我在

收到错误

delete from enrollments where sid = v_sid and classid = v_classid;

as Trigger无效且重新验证失败。

谁能告诉我究竟是什么错？