"ORA-01017: invalid username/password" while connecting to an instance remotely as sysdba

Seems simply a password issue. Different instances may have different passwords, the SYS password is not necessarily the same for all the instances on the same server. Make sure remote_login_passwordfile is configured properly in the instances, and the password file exists for instance SID1 on the server in ORACLE_HOME/dbs/orapwSID1 (Linux-Unix) or ORACLE_HOME/database/pwdSID1.ora (Windows).

If you do not know the correct SYS password, you can recreate the password file, for example:

orapwd file=$ORACLE_HOME/dbs/orapwsid1 password=xxxx force=y

From Oracle ORA-01017 tips by Donald Burleson:

Checklist for ORA-01017 errors:

The core issue with an ORA-01017 error is an invalid user ID and passwords combination, but other than an incorrect password, there are user ID issues that may contribute to the ORA-01017 error:

• It may be that the user ID is invalid for the target system - The user ID exists as the username column in the dba_users view.

  select username from dba_users;
  

• Check your $ORACLE_SID environmental parameter. If your $ORACLE_SID is set to the wrong system ID then you may get a ORA-01017 error because you are connecting to the wrong database.

• If using external OS user authentication (ops$ or remote_os_authent) you need to verify that the user ID is valid. You can tell if you are using external authentication because you connect without providing a user/password combination, and only provide a forward slash to the connect string, (e.g. connect / as sysdba;).

• Check your tnsnames.ora to ensure that the TNS service name points to the correct server and instance name. If you specify an incorrect tnsnames.ora service name, then the user ID and password may not exist in that database.

You can find extra information in the SAP on Oracle discussion ORA-01017: invalid username/password; logon denied