Multiple Invoices for one receiving slip

SOLVED

I had a receiving slip with multiple inventory items and they were invoiced to us on two invoices. When I posted the first PO invoice, I changed the Quantity Invoiced column to zero for the items that were on the second invoice. After I posted, I started to post the second invoice but no items are left when I entered the Receipt Number. Checking the GL Batch, it has also credited inventory by the amount of the items I entered as zero on the first invoice. What is the best way to correct this?