Purchase Order Budget Checking goes into Error

We are in FSCm 9.2. We created a Requisition in eProcurement and budget checked the requisition. Budget Status was valid. We executed the PO Auto Sourcing process to create Purchase Orders from this Requisition. Purchase Orders were created fine without any problem but the budget checking process gave an error with following error message -Predecessor Not Found - RefDoc

I will appreciate any help as I have never seen this error before and also I am confused that the Requisition with the same chartfields and amount did not fail budget checking then why the PO is failing budget chaecking.