ORA-20000: ORU-10027: buffer overflow, limit of 10000 bytes
ORU-10027 will appear if you are using a lot of dbms_output.put_line in your PL/SQL with a small buffer amount. If you are just debugging then you should set this to a large amount (dbms_output.enable(10000000) is traditional though from 10g onwards it can be unlimted: dbms_output.enable(null)) but try to remove them when going to production.