Hi Andres,
I think it's a core BPC and BW SP issue. What SP you have? On my system the code:
*XDIM_MEMBERSET MEASURES=PERIODIC
*WHEN CONCEPTO
*IS *
*REC(EXPRESSION = [MEASURES].[YTD]
*ENDWHEN
Works fine!
"We're not using an standard time dimension" - can show show it?
Vadim