BPC SCRIPT LOGIC TIME DIMENSION PROBLEM

Hi Experts,

I'm on BPC 10 MS SP13, with EPM-ADD SP18

I've a problem with script logic: I need a data region with two periods : Period Selected from prompt and Same Period Last Year.respect to selected period.

I try to use %YEAR%(-1) or %PERIOD%(-12) but in time dimension I have other elements , see below images.

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I try with this syntax:

*SELECT (%PREV_YEAR%,"PY",TIME,[ID]='%TIME_SET%')

*SELECT (%MONTH%,"[PERIOD]","TIME","[ID]='%TIME_SET')

*XDIM_MEMBERSET TIME=%PREV_YEAR%.%MONTH%,%TIME_SET%

When I check log i found that %PREV_YEAR% and %MONTH% are empty. Data in fact table are filtered only for %TIME_SET% .

If I substitute %TIME_SET% with fixed values (Ex: 2014.AUG )  %PREV_YEAR% and %MONTH% are populated correctly.

Any help appreciated

Thanks

Samuele