备份时的出错信息的片段如下：

validation succeeded for archived log
archive log filename=/oradata/IFXPROD/arch1/IFXPROD_1_2180.arc recid=4358 stamp=588573189
validation succeeded for archived log
archive log filename=/oradata/IFXPROD/arch1/IFXPROD_1_2181.arc recid=4360 stamp=588578555
Crosschecked 2 objects

Starting backup at 24-APR-06
channel t1: starting full datafile backupset
channel t1: specifying datafile(s) in backupset
waiting for snapshot controlfile enqueue
cannot make a snapshot controlfile
released channel: t1
RMAN-00571: ===========================================================
RMAN-00569: =============== ERROR MESSAGE STACK FOLLOWS ===============
RMAN-00571: ===========================================================
RMAN-03009: failure of backup command on t1 channel at 04/24/2006 12:56:49
ORA-00230: operation disallowed: snapshot controlfile enqueue unavailable

查看matalink后可以确认是因为有enquen lock存在，相关的SQL如下：

select s.sid, username, program, module, action, logon_time, l.*
from v$session s, v$enqueue_lock l
where l.sid = s.sid
and l.type = 'CF'
and l.id1 = 0
and l.id2 = 2

我是能过kill上面查得的SID后，再重做backup来解决的。更详细的内容可以查看下面的两个link(需要有metalink的帐号)：