Oracle Error Message
ORA-16191: Primary log shipping client not logged on standby
Reason for the Error
An attempt to ship redo to standby without logging on to standby or with invalid user credentials.
Solution
Check that primary and standby are using password files and that both primary and standby have the same SYS password. Restart primary and/or standby after ensuring that password file is accessible and REMOTE_LOGIN_PASSWORDFILE initialization parameter is set to SHARED or EXCLUSIVE.