Requisition Import Errors

In 12.1.3, a buyer is releasing planned orders from the workbench.  In many cases, these are showing up in the Requisition Import Exceptions Report with the following errors:

DELIVER_TO_REQUEST The requester is not an active worker
                                 Cause:        You entered a requester who is not a valid worker.

                                 Enter:          Enter a requester who is a valid worker.

PREPARER_ID        Preparer is not an active worker

                                 Cause:        You entered an inactive worker as the preparer.
                                 Action:        Enter an active worker as the preparer.
                                 Action:        Make the preparer an active worker.

For these exceptions, the preparer_id and deliver_to_requestor_id are both null.  What is populating these fields?  I assume that to avoid the errors, I will need to populate these with an active worker's ID somehow.