Problem Using Previous Month and Calculate in DAX

Hi,

I'm relatively new to DAX, but I'm just trying to put together a simple measure that takes the month-end inventory for a bunch of part numbers and sets it equal to the next month's beginning inventory. The month-end inventory is data in a data table. I have set up a couple measures that are meant to use the starting inventory, but since I can't get the starting inventory to work, none of my other measures are giving me correct numbers. In my attached file, I'm not getting an error for the starting inventory measure, but it's also not returning any values (see Sheet 1). Any help is appreciated!