Invalid Line Balance

I create an invoice. The invoice amount is 0. I create a credit memo, and I add the miscellaneous invoice. For each line on my invoice, I add the unitprice, for example my line 1 is 1 quantity * 2000$ my extprice is 2000. I add the misc charges -2000. I will need the invoice with 0 amount.

But when I print my edit list, I have this message : Invalid Line Balance. I don't know why ? My Invoice balance is 0