配置ogg downstream抽取时，注册抽取进程失败，请问是什么原因？

miss_puff

GGSCI (datahub) 2> info credentialstore

Reading from credential store:

Default domain: OracleGoldenGate

  Alias: downstream
  Userid: oggadmin@downstream

  Alias: source
  Userid: oggadmin@source

  Alias: target
  Userid: oggadmin@target

GGSCI (datahub) 3> dblogin useridalias source
Successfully logged into database.

GGSCI (datahub as oggadmin@orcl2) 4> miningdblogin useridalias downstream
Successfully logged into mining database.

GGSCI (datahub as oggadmin@orcl2) 5> register extract extorcl database

2019-03-22 15:31:48  INFO    OGG-15419  Standby Redo Logs were not detected on the downstream database.

2019-03-22 15:32:30  ERROR   OGG-08221  Cannot register or unregister EXTRACT EXTORCL because of the following SQL error: OCI Error ORA (status = 23605-ORA-23605: invalid value "1763072" for GoldenGate parameter start_scn
ORA-06512: at "SYS.DBMS_XSTREAM_GG_ADM", line 145
ORA-06512: at "SYS.DBMS_XSTREAM_GG_ADM", line 186
ORA-06512: at line 1
).

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