Inner Select Column Field

Dear all,

I have problem in the following SQL. Please help. The problem in the inner select statement for the group by clause. Please help

select company.billtocompany,
(select quartername from quarter where a.orderdate between
convert(datetime, quarter.startdate) and convert(datetime, quarter.enddate)+1) quartername,

sum( a.qty) orderedqty

from a, company, countrycode

where a.billtocompany=company.compcode and
a.countrycode=countrycode.countrycode and
a.billtocompany='111111' and
a.orderdate between convert(datetime, '2008/01/01') and convert(datetime, '2008/10/01')

group by company.billtocompany, countrycode.countryname, quartername