Has anyone seen this error before on Customer Refunds? Obviously no line items to enter or check for

Pretty sure that's referring to having to apply the customer refund to an open credit memo or credit balance (via JE) on that customer's account

hmm.. interesting

There's a bug too in one of those sublists thats due to post sourcing of the header level item that causes the item sublist to select a new line thinking something is going to be entered. You have to add a client script to grab the line and cancel it as a workaround or it will always pop up the dialog.