error ORA-09817: Write to audit file failed. / ORA-00257: archiver error. Connect internal only, until freed.

When you try to login as sys using sys/password as sysdba, you may get the error ORA-09817: Write to audit file failed.

And If you tried to login as a normal user you may get  the error - ORA-00257: archiver error. Connect internal only, until freed.

These errors are giving most probably because your Archive destination is full.

Check archive destionation : 

SQL> ARCHIVE LOG LIST
Database log mode              Archive Mode
Automatic archival             Enabled
Archive destination            USE_DB_RECOVERY_FILE_DEST
Oldest online log sequence     1324060
Next log sequence to archive   1324066
Current log sequence           1324066

SQL> show parameter DB_RE

NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
db_recovery_file_dest                string      /u01/app/oracle/flash_recovery_area
db_recovery_file_dest_size           big integer 2000G

Try to check the free space with Linux commands (# df -h) and free up space in Archive location.

Better to put a cron job to delete old archives leaving up to 3-4 days archives in your database.