you are not setup as a buyer

You are not setup as a worker. To access this form you need to be a worker EBS R12.2.4

This USER ID -should have assigned proper employee from HR Module.

 HR Navigation: (Human Resources>> People>> Enter and Maintain), Person types should be ‘employee’ now.

Assigning Employee to User ID:

Add this new employee to your user name ( System Administrator>> Security>> User>> Define ), Add newly created employee in the person field.

Define this Employee as  BUYER (OAF page will open)

Adding a new buyer ( Purchasing>> Setup>> Personnel>> Buyers),Click Add Buyer button and search for your newly created employee and select it and save it. New buyer is added.