Excel OLAP MDX Measure to Retrieve Prior Year Same Period

Question

I'm working with an OLAP Cube in Excel and I'm trying to pull the PY number in the current year (example below).

I've tried using something similar as was suggested here: MDX Formula with Excel OLAP-Extension

AGGREGATE([Shift Date].[Week Number].CurrentMember.Lag(52), [Measures].[Total Rate])

However, it wasn't working at all; all I got was '#VALUE!'

I also tried the following:

SUM(PARALLELPERIOD([Shift Date].[Week Number].CurrentMember, 52), [Measures].[Total Rate])

But, again, all I got was '#VALUE!'

Is there something I am missing? What am I doing wrong?