Purchasing Defaults screen is no longer available
The Purchasing Defaults screen was removed from the software's design. The settings contained within that screen were either not useful or problematic.
The default PO prefix was essentially a useless setting. PO prefixes, as well as the setting of a default PO type, is already specified under (Purch > Purchasing Setup > PO Types).
The "Next PO Number" and "Next PO Receipt Number" settings were removed because they were causing large problems with collisions, overlapping numbers, and MRP. The software, instead, will assign its own number to these internally.