之前多次执行相同步骤恢复数据库，没有如下的报错。请专家帮忙分析一下，是备份集问题吗？最后不得已使用在线duplicate完成异机恢复。

executing Memory Script

Errors in memory script
RMAN-03015: error occurred in stored script Memory Script
RMAN-06136: ORACLE error from auxiliary database: ORA-01507: database not mounted
ORA-06512: at "SYS.X$DBMS_RCVMAN", line 14891
ORA-06512: at line 1
RMAN-03015: error occurred in stored script Memory Script
RMAN-20000: abnormal termination of job step
RMAN-06054: media recovery requesting unknown archived log for thread 2 with sequence 1830 and starting SCN of 5971507039567
RMAN-00571: ===========================================================
RMAN-00569: =============== ERROR MESSAGE STACK FOLLOWS ===============
RMAN-00571: ===========================================================
RMAN-03002: failure of Duplicate Db command at 03/27/2019 01:55:01
RMAN-05501: aborting duplication of target database