create sequence num
start with 1
increment by 1
nomaxvalue 
nocycle
create table OneCard
(
id number not null,
createdate date,
value varchar(50)
)
insert into OneCard(id,createdate,value) values(num.nextval,to_date('2012-10-23 8:00:00'),'30')

insert into OneCard(id,createdate,value)
values(num.nextval,to_date('2012-10-23 8:00:00','yyyy-mm-dd hh24:mi:ss'),'30');

------解决方案--------------------
楼上是正解，你的日期格式化有错误。
你查询一下这两条SQL 你就明白了...[code=SELECT] to_date('2012-10-23 8:00:00') FROM dual; 
 SELECT to_date('2012-10-23 8:00:00','yyyy-mm-dd hh24:mi:ss') FROM dual; 
 [/code]

------解决方案--------------------
楼上正解，建议楼主先熟悉一下TO_DATE函数。