I'm always getting this error : "WEBTOPATTACHEDFILECAPACITY" as a column".

I've a small procedure

CREATE OR REPLACE procedure conf_malay as
cursor c1 is
select zonename,WEBTOPATTACHEDFILECAPACITY from configuration_temp;
begin
FOR c1_rec IN c1 LOOP
update zone set WEBTOPATTACHEDFILECAPACITY= c1_rec.WEBTOPATTACHEDFILECAPACITY
where zonename=c1_rec.zonename;
end loop;
commit;
end;
/

It compiled successfully.

But i changed one of it's column WEBTOPATTACHEDFILECAPACITY as default and not null by this SQL

alter table zone add WEBTOPATTACHEDFILECAPACITY varchar2(4000) default '500000000' not null

After that when i compile this procedure it always gave me that error message.

Any idea..