SQL 错误: ORA-06575: 程序包或函数 处于无效状态

[LUCKY桉桉小怪兽。]

create or replace function f_nopassNumByCno(f_cno course.cno%type)
return number as
num number;
name char(10);
begin
  select cname into name from course where cno=f_cno;
  select count(*) into num from course where grade<60 and cno=f_cno;
  dbms_output.put_line(name||'未及格人数'||num);
  return num;
end;
/

select f_nopassNumByCno(2) 不及格人数 from dual;

程序代码如上，运行体式SQL错误。求解！万分感谢。