Why won't P3 calculate my activity duration?

Hello.

I'm a novice working with P3.  I have an existing project with many activities with assigned durations and logic.  I want to add a resource, specifically cubic yards of material, and assign it to the activities with a budgeted quantity of cubic yards to complete.  I want to enter a defined units/time period to calculate the activity duration.

My problem is that in the resource box, I can enter the quantity, but when I enter the units/time period, everything defaults to 0...for every activity.  Don't know why.  But, when I add a completely new activity to the schedule, all operations seem to work fine...the budgeted quantity, the units/time period and the new activity duration will calculate.

Help with understanding this is appreciated.