So just to give you an example of how our procedure would eventually work with data and come up with this error, here's some SQL:
DECLARE @daysInPeriod INT
DECLARE @dcFraction DECIMAL(38,38)
DECLARE @YEAR_360 DECIMAL
SET @YEAR_360 = 360.0000000000
SET @daysInPeriod = DATEDIFF(dd, '12/24/1970', '6/29/07')
SET @dcFraction = @daysInPeriod/@YEAR_360
If you run this in SQL Server 2008 R2, you'll see that you receive an 'Arithmetic overflow error converting numeric to data type numeric.' error.
The decimal that I am setting the value to is max'd out in terms of places it can hold, which I believe is 38. I don't know what else I can do to get this value. Shouldn't you be able to divide an integer with a decimal in SQL and get something out of it, especially if the decimal is max'd out?