First of all, this query cannot work :
Select MAX(itemno), title into num, new_title from item;
=> ORA-00937: not a single-group group function
Rewrite it as :
select itemno, title into num, new_title from item where itemno = (select max(itemno) from items)
About the error message : ORA-01422: exact fetch returns more than requested number of rows. It means exactly what it means. A "SELECT INTO" query can only return 0 or 1 row, not more. Declare your select as a cursor, and process on a row-by-row basis.