MAX() returns #MULTIVALUE in BO 4.1

Hi,

I've got strange issue when using max() function - it returns #MULTIVALUE error.

I've got following data

Country, ProductID, ProductDate

C1,1,01/01/2014

C1,2,01/02/2014

C1,3,01/01/2013

...

Now I've got DateCalc

DateCalc is variable and DateCalc = MonthsBetween([ProductDate];CurrentDate()) ForEach(ProductID)

Now I want to calculate max of that DateCalc in that way:

Country, max([DateCalc] where ([DateCalc] <= 1))

and I'm getting multivalue errors in max column.

Could you please suggest any solution?

Many thanks and regards