Date In String Doesn't Work

Can anyone please tell me why this query works:


DECLARE @valuation_date smalldatetime, @non_admit_date smalldatetime
SET @valuation_date = '2006-03-31'
SET @non_admit_date = DATEADD(dd, -90, @valuation_date)
SELECT SUM(Premium) FROM Reserves WHERE Reserve_Paid_to_Date >= @non_admit_date

And this one does not:

DECLARE @valuation_date smalldatetime, @non_admit_date smalldatetime, @arc_sql nvarchar(4000)
SET @valuation_date = '2006-03-31'
SET @non_admit_date = DATEADD(dd, -90, @valuation_date)
SET @arc_sql = 'INSERT INTO Results SELECT SUM(Premium) FROM Reserves WHERE Reserve_Paid_to_Date >= ' @non_admit_date
SELECT @arc_sql
exec sp_executesql @arc_sql



The second one gives me this error: "Syntax error converting character string to smalldatetime data type."

How can I run the second one? I need to dynamically build an Insert statement and this is stopping me.

Thanks!

-Ticia