Do you have the printout for the receipt of goods register? That's the first place to look for clues. Can you confirm it was actually updated?
You say the PO shows zero items in it. Their are three important quantities. Order, received and invoiced. Which quantity now shows zero?
Did anything post to the general ledger? Did anything post to A/P?

Actually all columns are showing zero quantity and yes items did post to the general ledger, just no update to the inventory.

Further follow up to your query.

It was received in "receipt of Invoice Entry" in error. Yes it went to general ledger and A/P. Deleted the P.O. and received in "Inventory Management Transaction Entry" The PO was then deleted.

Pardon for bumping this, but would anyone have an answer for my reply to the original post?

Thanks, Martin

Receipt of invoice would not update the inventory module. That just updates the AP and GL. Inventory Transaction receipt will not update the PO, just IM and GL. In order to delete the PO, you would have to have all columns zero or you would not be able to delete it from the user interface. I have only seen 2 situations where the PO did not get updated from a receipt of goods or receipt of invoice as designed. 1) Required UDF setup and the field was blank 2) error received during update. I have also seen some strange behaviors when entering multiple receipts for the same PO in the same update but not this. Unless this can be recreated at will we may not be able to determine what exactly happened to this PO.