Looking at your query the from clauses and where clauses don't quite make sense to me.
Code:
(SELECT COUNT(*)
FROM DM.PMT
WHERE CLT230_VIEW.CLT_ID = PMT.CLT_ID
AND DATEFORMAT(PMT_DATE,'YYYY-MM') = PERIOD)
AS NBR_ACCTS_PAID
In the above subquery you have DM.PMT in the From Clause. but in the where clause you have PMT.CLT_ID In the main from clause you again have the DM.CLT230_View but leave of the DM. in the Where of the sub query. It may not make a difference but it's been my experience that the Table portion of the Select, Where, Group by and Order by should match the from.