Year to date prior year

Hello,

I have used the time intelligence wizard in VS 2008 BIDS to add time intelligence to both my date dimension and a cube.  One of the calculated members it created in my cube is defined -

Create Member 
  CurrentCube.[Date].[Year-Month-Date Calculations].[Year to Date] 
  As "NA" ;

// Year to Date
  (
    [Date].[Year-Month-Date Calculations].[Year to Date],
    [Date].[Year].[Year].Members,
	[Date].[Date].Members 
  ) 
  
  =

  Aggregate(
             { [Date].[Year-Month-Date Calculations].[Current Date] } 
             *
             PeriodsToDate(
                            [Date].[Year-Month-Date].[Year],
                            [Date].[Year-Month-Date].CurrentMember
             )
  ) ;

This works perfectly.

I want to modify this so that i have "Year to Date Prior Year" member using the ParallelPeriods function with no luck. What i want is member that will calculate the year-to-date for same date 1 year before the curretly selected date.   I have researched this and read other posts on this forum and tried everything I can think of.   The following MDX always returns null even though I know it is not in the data

ParallelPeriod([Date].[Year-Month-Date].[Year], 1, [Date].[Year-Month-Date].CurrentMember);

Any advice as to why this is so would be appreciated!

Also, why is there a multiplication (*) inside of the aggregate function in the wizard generated code?

Thanks