This is interesting. :)

The letters act are used for the VFP to control the workarea. Thus, d.StartDate is the same that

select d
? StartDate

and not a propertie of object D

Replace the letter 'D' for 'Z' and will function.

See manual:

Select cTableAlias

cTableAlias
Specifies a work area containing an open table to activate. cTableAlias is the alias of the open table. You can also include a letter from A through J for cTableAlias to activate one of the first ten work areas.