Cannot group that selection in a pivot table

dharbison For the grouping to work ALL rows must be dates or truly  blank. And when you have blanks, the will show up in a group "less than the earliest date in the list". See picture below.

Since you mention that the date column is calculated, I assume you have formula that returns either a date or and empty string (""). An empty string is NOT blank. That's why you see the item with no label and you can not group de dates anymore.