I assume the database schema in question might have been refreshed with another instance and these errors are quite common in such scenarios when Online back up is taken.
You can run below query and see what is the next sequence number being generated
select CMN_AUDITS_S1.NEXTVAL from dual
and then run below query to see what is the last sequence number used
select MAX(ID) from CMN_AUDITS
You should observe that result from query 1 is less than that of query 2. If so, modify the sequence CMN_AUDITS_S1 to ensure the next number is greater than result from query2