Select Statement inside of

Question

I get error "Subquery returned more than 1 value. This is not permitted when the subquery follows =, !=, <, <= , >, >= or when the subquery is used as an expression." When I set @MonthYear = 2. = to 1 it work just as I want it. What can I change here?

insert into #LoansTable (Year ,LoanType,ProcessDate ,Month ,Balance ,RowNum, PercentChange, LastCol
    )
select 
x.YEAR,LoanType,ProcessDate,Month,Balance,RowNum

--,Cast(SUM( Balance - LastCol )/LastCol  * 100  as nvarchar(20)) +' ' +'%' as PercentChange

,case when LastCol = 0 then 0
else SUM( Balance - LastCol )/LastCol  * 100  
end as PercentChange
, LastCol
from
(
SELECT *,
    
case when @MonthYear = 1 then isnull(LEAD(Balance,1) over (order by rownum),2)
When @MonthYear = 2 then (select balance from #MonthlyLoanBalance2 where ProcessDate = convert(Varchar(8),DATEADD(ms,-3,DATEADD(yy,0,DATEADD(yy,DATEDIFF(yy,0,GETDATE()),0))),112))
end as LastCol

FROM #MonthlyLoanBalance2


)x
Group by x.YEAR,ProcessDate,Month,Balance,RowNum,Loantype,LastCol
order by year desc, RowNum

Select * from #MonthlyLoanBalance2

My code I want to pull the last day of the previous year based on toggle that I setup in another reporting system. If 1 it will return the prevous Month end of month balance. If 2 then it will return previous years end of month balance. (December 31st) Previous month works as desired. Just need the previous years end balance so my other calculations work.