If you can reproduce this state of data for a new requisition, then please get exact steps to reproduce and log an SR.
If this issue is unique for this REQ/PO, then it is assumed that the PO is not yet approved because of the missing account errors.
You may take this approach to resolve this unique issue:
1- Delete the PO - PO should be in Incomplete in this state thus allowing for deletion
2- Once PO is deleted, the REQ is no longer tied to the PO. Expect the requisition in Approved status at this time. Cancel for Finally Close the req.
3- Create new one to replace.