This is an error generated in Walmart's system (this could be Walmart USA, Walmart Canada, or Sam's Club) regarding an issue with invoice totals you have sent to them recently in an Invoice EDI document. This invoice has been rejected.
When creating your invoices for Walmart the Invoice total must be greater than zero and the total must be calculated from the total of your item's price multiplied by the quantity shipped. If there are any allowances or charges (shipping charge, promotional allowance) you can indicate them on the summary tab. These amounts will also apply to your invoice total. You should make sure that you are pressing the "+" button to add items from the purchase order onto your invoices. If you didn't ship an order, you do not need to send them an invoice with zero quantities on it.
When you are ready to re-send, you would follow the same procedure in WebForms as when you sent this document.