When press PO invoice button, there is an error.
Therefore, I try to delete invoice in AP > invoices > pending invoices
(ref : http://axaptaexplorer.blogspot.com/2013/04/how-to-delete-pending-invoices.html , Thanks very much for short and effective blog )
In my case, TransDate was missing from the Network down. Therefore, the exchange rate cannot be get for the (blank) date
Therefore, I put TransDate and then go to remove as normal case AP > invoices > pending invoices