partition by not working in procedure

alter procedure dbo.d
as begin
  declare @TotalPickedUp int  =0
 set @TotalPickedUp=((  SELECT count(*)
FROM   (
         SELECT c.courierid
                , rn = ROW_NUMBER() OVER (PARTITION BY cs.courierid ORDER BY date DESC)
         FROM   courierstatus_tracker cs inner join courier c on c.courierid=cs.courierid
          where  cast(c.courierdate as date)='2014-07-24 00:00:00.000'  and
 (cast(cs.Pickedup_ActualDate as date)<=cast('2014-07-28 00:00:00.000' as date)
 or cast(cs.date as date)<=cast('2014-07-28 00:00:00.000' as date)
 ) and
 c.Productorservices='Reverse Pickup'  and cs.reasonid>=31) bt
WHERE  rn = 1))

select @TotalPickedUp  as data
end