dataguard模式下主备机切换，切换后主机警告日志错误：
*** 2009-03-27 09:35:29.000
kcrrfail: dest:2 err:16009 force:0
ORA-16009: remote archive log destination must be a STANDBY database
*** 2009-03-27 09:49:51.000
Error 16009 attaching RFS server to standby instance at host 'standby'
Error 16009 attaching to destination LOG_ARCHIVE_DEST_2 standby host 'standby'
Heartbeat failed to connect to standby 'standby'. Error is 16009.
*** 2009-03-27 09:49:51.000
kcrrfail: dest:2 err:16009 force:0
ORA-16009: remote archive log destination must be a STANDBY database
*** 2009-03-27 10:04:13.000
Error 16009 attaching RFS server to standby instance at host 'standby'
Error 16009 attaching to destination LOG_ARCHIVE_DEST_2 standby host 'standby'
Heartbeat failed to connect to standby 'standby'. Error is 16009.
*** 2009-03-27 10:04:13.000
kcrrfail: dest:2 err:16009 force:0
ORA-16009: remote archive log destination must be a STANDBY database
*** 2009-03-27 10:18:35.000
Error 16009 attaching RFS server to standby instance at host 'standby'
Error 16009 attaching to destination LOG_ARCHIVE_DEST_2 standby host 'standby'
Heartbeat failed to connect to standby 'standby'. Error is 16009.
*** 2009-03-27 10:18:35.000
kcrrfail: dest:2 err:16009 force:0
ORA-16009: remote archive log destination must be a STANDBY database
- Created archivelog as 'E:\ARCHIVE\RAC_1_05914.ARC'

请帮忙分析原因