I need to calculate Inception To Date (I

I need to calculate Inception To Date (ITD) measure, just like the YTD but this one will span over multiple years. My Date dimension has a hierarchy like this..Calendar Year, Calendar Quarter,Calendar Month..and I tried to use the PeriodsToDate function, but its telling me, I used member expression instead of level expression.. Below gives me YTD amount... Aggregate ( PeriodsToDate ( [AC Period].[AC Period Hierarchy].[Calendar Year], [AC Period].[AC Period Hierarchy].CurrentMember ), [Measures].[Gross Actual Amount] ) And I tried..for ITD amount Aggregate ( PeriodsToDate ( [AC Period].[AC Period Hierarchy].[All], [AC Period].[AC Period Hierarchy].CurrentMember ), [Measures].[Gross Actual Amount] ) I appreciate your help in advance..