You need to move SUM outside the case, e.g.

select  [date], count(data.vou_no) as tot,
SUM(case when data.type=1  then data.vou_no end) as ac_cr,
SUM(case when data.type=2  then data.vou_no end) as ac_dr
	from (
	select count(vou_no)as vou_no,date, 1 as type  from vouchers where VOU_type='CR' and cr_amount>0  group by date
	union all
	select count(vou_no)as vou_no,date, 2 as type from vouchers where VOU_type='CP' and dr_amount>0 group by date
	) data
	group by [date]

>Hello Experts
>
>I have this query
>
>

>select max(DATE)as date, count(data.vou_no) as tot,
>(case when data.type=1  then sum(data.vou_no) end) as ac_cr,
>(case when data.type=2  then sum(data.vou_no) end) as ac_dr
>	from (
>	select count(vou_no)as vou_no,date, 1 as type  from vouchers where VOU_type='CR' and cr_amount>0  group by date
>	union all
>	select count(vou_no)as vou_no,date, 2 as type from vouchers where VOU_type='CP' and dr_amount>0 group by date
>	) data
>	group by date
>

>
>but this query does not work
>it says:
>Msg 8120, Level 16, State 1, Line 3
>Column 'data.type' is invalid in the select list because it is not contained in either an aggregate function or the GROUP BY clause.
>
>as shown in image
>
>How to overcome this?
>
>Please help