Check your level of security - if they are outside of your Cost Center or Cost Center Hierarchy, you would need Security Access at the Company level to process their PAA.
If their position has ended, or if they have moved to a position in another Company, you will not be able to create the PAA. You will need to request this from Central Finance. Until an official request process is created, do this by sending an email to AskFinance@virginia.edu with the instructions on what adjustment needs to be made.