Sense: Using a variable in set analysis

[Ri_ta]

Hey guys,

I have two variables in my script:

LET vYearMonthCurrent = '=Max(YearMonth)';
LET vYearMonthPrevious = '=Date(Addyears(Max(Id_Date), -1), '&chr(39)&'YYYY-MMM'&chr(39)&')';

And I'm using the first one in a graph in set analysis in this expression:

SUM ({<YearMonth= {"$(vYearMonthCurrent)"} >}VALUE)
+
SUM ({<YearMonth= {"$(vYearMonthCurrent)"} >}VALUE_AC)

It works just fine.

But if I want to use the variable with the previous year&month and do this:

SUM ({<YearMonth= {"$(vYearMonthPrevious )"} >}VALUE)
+
SUM ({<YearMonth= {"$(vYearMonthPrevious )"} >}VALUE_AC)

It shows 0.

Do you know why this happens?

Thanks,

Rita