出现ORA-16191错误的原因有哪些？

创建DG后，主库无法传日志文件到备库，TRACE文件内容如下：
*** 2013-03-27 19:32:24.367
OCISessionBegin failed. Error -1.. Detailed OCI error val is 1031 and errmsg is 'ORA-01031: insufficient privileges'
OCISessionBegin failed. Error -1.. Detailed OCI error val is 1031 and errmsg is 'ORA-01031: insufficient privileges'
OCI_DBVER attribute value retrieval failed error=1017
*** 2013-03-27 19:32:24.717 4320 krsh.c
Error 1017 received logging on to the standby

------------------------------------------------------------
Check that the primary and standby are using a password file
and remote_login_passwordfile is set to SHARED or EXCLUSIVE,
and that the SYS password is same in the password files.
returning error ORA-16191

------------------------------------------------------------
*** 2013-03-27 19:32:24.717 915 krsu.c
Error 16191 connecting to destination LOG_ARCHIVE_DEST_2 standby host 'STBY'
Error 16191 attaching to destination LOG_ARCHIVE_DEST_2 standby host 'STBY'
*** 2013-03-27 19:32:24.717 4320 krsh.c
PING[ARC2]: Heartbeat failed to connect to standby 'STBY'. Error is 16191.
*** 2013-03-27 19:32:24.717 2932 krsi.c
krsi_dst_fail: dest:2 err:16191 force:0 blast:1


那一般有哪些原因导致这个ORA-16191错误呢