ORU-10027 error caused by DBMS_OUTPUT calls in a function

I received the following error when I converted a stored procedure (with DBMS_OUTPUT.PUT_LINE calls) to a function.

ORA-20000: ORU-10027: buffer overflow, limit of 2000 bytes
ORA-06512: at "SYS.DBMS_OUTPUT", line 106
ORA-06512: at "SYS.DBMS_OUTPUT", line 65
ORA-06512: at "TWS.PRIOR_HISTF", line 49
ORA-06512: at line 1

I understand these calls are inappropriate in a function...and have been removed...however, some questions did come to mind... Where are these ORU-XXXXX messages documented? Would adding the call DBMS_OUTPUT.ENABLE(100000) resolve this error? Where was the output going? Was is retrievable from some buffer or other location?
Why don't you see the output when the function is run in SqlPlus (as from a stored procedure) with Set Serveroutput On?

Thanks for your assistance.
Don Hall
Transworld Oil USA Received on Tue Jul 13 1999 - 15:15:44 CDT