set analysis error

[arusanah]

I'm trying to use this expression to find previous year sale .

=Sum({$<TimeLine.Year={$(=(TimeLine.Year)-1)}>}(Fact.CustomerSales*[CurrencyConversion.USD - Budgeted Rate CFY]))

when i execute this expression it displays zero . where as i do have sales for that year . i'm defn missing something in this expression ... but im not able to figure out .

pls help

[maxgro]

=Sum({$<TimeLine.Year={$(=max(TimeLine.Year)-1)}>}(Fact.CustomerSales*[CurrencyConversion.USD - Budgeted Rate CFY]))