Excel Help states that I should be able to use the Subtotal command under the
data menu with an Excel List (created with the Create List command under the
Data menu). When I create the list and then attempt to use subtotal, the
option is grayed until I convert the list back to a standard range.....Can
anyone tell me what I am doing wrong. Help text is below:

Microsoft Excel can automatically calculate subtotal and grand total values
in a list (list: A series of rows that contains related data or a series of
rows that you designate to function as a datasheet by using the Create List
command.). When you insert automatic subtotals, Excel outlines the list so
that you can display and hide the detail rows for each subtotal.