Workdays Dax not working

Hello -

I have two tables - CalendarData & tblrma

CalendarData = Date table (Has a IsWorkday calculated column)

tblrma = facts table (Have total of 2 date fields that need checked)

The below DAX works in PowerPivot but does not work in PowerBI Desktop.  The error is: An invalid numeric representation of a date value was encountered.

= IF(AND([EstEmpty] = FALSE(), [POEmpty] = FALSE()),
        CALCULATE(Sum('CalendarData'[IsWorkday]),  
              DATESBETWEEN(CalendarData[Date], [estimatedate], [podate])), 
        Blank())

EstEmpty = test for blank (Checks for blank returns true false)

POEmty = Test for Blank (Checks for blank returns true false)

Any help is appreciated!

Raven