This issue comes because you did not mentioned the Ledger accounts (Chart of accounts) at Item group form. First you need to create the Chart of accounts at GL > Common forms > Chart of accounts.
Now, go to Item group form (Inventory management > Setup > Item group > Sales order Tab) … here in sales order tab, you need to assign the ledger accounts for Packing slip, Packing slip offset and Packing slip revenue, Packing slip revenue- offset accounts along with these Issue, Consumption, revenue, Discount accounts as well. Discount account is optional. If you’re giving discount at SO line then you need to have this discount account.