Follow the steps below for handle the error when the error message is prompted.
1) Refer to the error message and see what the problem is occurred
For example, when you post the purchase order, system prompted the error message "Purch. Inv. Disc. Account must have a value in General Posting Setup: Gen. Bus. Posting Group = xxx, Gen. Prod. Posting Group = xxx...."
That means your purchase order or invoice has discount and the discount posting option in Purchase & Payable setup is selected All Discount or Invoice Discount
However, the G/L account for Purchase Invoice Discount is missing in General Posting Setup.
2) Check the Gen Bus Posting Group of the vendor (Vendor Card) for the PO and check the Gen Prod Posting Group for the item (Item Card) it recorded in purchase line.
3) Find the combination of the posting group in general posting setup and then select the Purchase Invoice Discount Account from Chart of Account.
4) Go back to the Purchase Order and then use Preview Posting Function to check if the Entry after post is expected or not.
5) If the G/L account that the entry post to is expected, then Post the Purchase Order.