function refuses to work in where clause??

I've got this function that tells me when a customer's last few orders had rejected credit cards transactions in our orders table.

When I run the fuction against dual manually plugging in the account number which is the only parameter to the function it returns a 1 telling me the customer qualifies. However, if I include the function in a select where plugging in the account number from the select, it never finds any rows.

Thanks for any help or information.

my function:

REATE OR REPLACE FUNCTION IS_REJECTING_Fn(iaccount_number in number) RETURN number

 AS
bad_count number;
vlast_update date;

begin
select count(*) into bad_count from (select * from (select * from orders o where o.ACCOUNT_NUMBER=iaccount_number order by o.VALIDATION_DATE desc)
 where rownum <4) where status=-20 ;

select last_update into vlast_update from  autorecharge a where a.account_number=iaccount_number;

if (bad_count=3) and (vlast_update<sysdate-3 or vlast_update is null) then
  return 1;
else
  return 0;
end if;

END Is_Rejecting_fn;

It returns a 1 here:

select is_rejecting_fn(2408) from dual

this code pulls many rows including one with account_number 2408

select * from orders o where trunc(o.validation_date) > '14-Oct-2007' and status=-20

This pulls nothing:

select * from orders o where trunc(o.validation_date) > '14-Oct-2007' and status=-20 and
  is_rejecting_fn(o.account_number)=1 Received on Mon Oct 15 2007 - 16:38:26 CDT