Pending Invoice Exists but does not Exits
Sometime in AX the pending invoice button is active but there is no pending invoice, and if you try to make a new invoice you will normally get this message.
A pending invoice cannot be displayed because it is in use. If nobody else is working with the invoice, you can delete the unconfirmed changes to the invoice, and then you can modify the invoice. Use the Invoice history and matching details form or the Approval journal history and matching details form to delete the unconfirmed changes.
to resolve this issue You need to find the table VendInvoiceInfoLine and in the table find OrgiPurchId find your PO number. Then delete that record. Next step is to find the table VendInvoiceInfoTable and then in that table find PurchId, find your PO number and delete that record as well.
This should clear up the issue
for more issues https://ashdynamicsax.wordpress.com/2017/06/18/post17-pending-invoice-issues/ follow this link.