Recently I got this error when I tried to execute a script with lots of dbms_output lines in it and the solution was to alter the script and to add the following:

 SET LINESIZE 999
 SET PAGES 500
 SET TIMING ON
 SET SERVEROUTPUT ON size UNLIMITED
 .........................
BEGIN
begin
 dbms_output.enable(NULL);
end;
.............................
END;
 /