metalink 解释是一个bug 4596065，只发生在Linux X86平台的Oracle 10.2.0.1.0下，而且只在11g里解决。这个并不是真正意义的error，可以不用管它,Just ignore it
bug 4596065 信息如下
------------------------------------------------------------------------------------------
Bug No. 4596065
Filed 07-SEP-2005 Updated 18-OCT-2005
Product Oracle Server - Enterprise Edition Product Version 10.2.0.1.0
Platform. Linux x86 Platform. Version No Data
Database Version 10.2.0.1.0 Affects Platforms Generic
Severity Severe Loss of Service Status Development to Q/A
Base Bug N/A Fixed in Product Version 11.0
Problem statement:
RMAN BACKUP GENERATES EMPTY TRACE FILES WHEN DB_RECOVERY_FILE_DEST IS SET