Receiving the following error in step failure of an agent job:
Annoying isn't it. I've done some research and it turns out it is incorrectly reporting a ANSI warning as an error (resolved in SQL Server 2012, no patch available for previous versions).

One way to stop the error is to go through all your code, and wherever you have an aggregate function (e.g. SUM), use ISNULL to ensure the aggregated value can never be NULL:

i.e. change 

SUM(Field1+Field2)


to 

SUM(ISNULL(Field1,0)+ISNULL(Field2,0))


This makes the error go away but might be impractical.