SOLVED: ORA-00257 archiver error. Connect internal only, until freed

Normally this error occurs when the space allotted for the archive logs has been exhausted

First backup the archivelogs
mv /u10/oradata/mydb/arch/* /u15/oradata/mydb/arch-bkp/

Log in to rman and delete  the archive log
rman target /
delete archivelog until time 'trunc(sysdate)';


You should be able to startup the database or log in to it after which you can
backup the database.

backup database;