This would do what you are looking for:

Select p.Month, SUM(p.cramount) As Credit, SUM(q.dramount) As Debit From

(

Select b.voucherno, DATENAME(MM, a.dt) As Month, SUM(b.cramount) As cramount From voucher As a

JOIN voucherCr As b ON a.voucherno = b.voucherno AND a.vouchertype = b.vouchertype

Group By b.voucherno, DATENAME(MM, a.dt)

) As p

JOIN

(

Select b.voucherno, DATENAME(MM, a.dt) As Month, SUM(b.dramount) As dramount From voucher As a

RIGHT JOIN voucherDr As b ON a.voucherno = b.voucherno AND a.vouchertype = b.vouchertype

Group By b.voucherno, DATENAME(MM, a.dt)

) As q ON p.voucherno = q.voucherno

Group By p.Month