Issue with an SQL having clause

I need to select records where the total of some fields is greater than zero. The field comparisons are from two different tables. Here is the sql:

select ixprod,ixdesc,extvin,(lqord-lqshp) as ordqty,
coalesce(sqreq-sqfin,0) as openSO
from fix inner join ecl on ixprod=lprod
inner join eclx01 on lord=extord and lline=exline
left outer join fso on ixprod=sprod
group by ixprod,ixdesc,extvin, (lqord-lqshp),
coalesce(sqreq-sqfin,0)
having ((coalesce(sqreq-sqfin,0)) - (lqord-lqshp)) > 0 <---- It doesn't like this line

I am running this in an interactive SQL session to test it and it is complaining about the SQREQ column in the having clause.

This DOES work:

select ixprod,ixdesc,extvin,(lqord-lqshp) as ordqty,
coalesce(sqreq-sqfin,0) as openSO
from fix inner join ecl on ixprod=lprod
inner join eclx01 on lord=extord and lline=exline
left outer join fso on ixprod=sprod
group by ixprod,ixdesc,extvin, (lqord-lqshp),
coalesce(sqreq-sqfin,0)
having coalesce(sqreq-sqfin,0) > 0

Yet with addition of one set of parenthesis in the having clause, it will stop working:

select ixprod,ixdesc,extvin,(lqord-lqshp) as ordqty,
coalesce(sqreq-sqfin,0) as openSO
from fix inner join ecl on ixprod=lprod
inner join eclx01 on lord=extord and lline=exline
left outer join fso on ixprod=sprod
group by ixprod,ixdesc,extvin, (lqord-lqshp),
coalesce(sqreq-sqfin,0)
having (coalesce(sqreq-sqfin,0)) > 0 <-----This will not work.

The reason for the parens is so that the having clause is properly evaluated, but I must be doing something wrong.

What am I missing?