How to provide the correct Return Value from the List of Value query in the BIP Data Model

Summary:

I have this BIP Data model which extracts the pending approval of a certain user. This used to work before but now I am getting this error "Invalid parameters requested." Below is the LOV SQL query:

select distinct dn.display_name,pu.username
from
per_users pu,
per_person_names_f dn
where
pu.person_id=dn.person_id
order by dn.display_name

The expected return value is pu.username.

Here is the BIP data model:

select
distinct title,
to_date(to_char(trunc(assigneddate,'mi'),'YYYY-MM-DD hh24:mi'),'YYYY-MM-DD hh24:mi') assigned,
fromuser,fromuserdisplayname,
processname,
(select distinct dn.display_name