Some times we face Purchase invoice creation and posting common error like blank invoice line,invoice no etc and its happen due to closing invoice form without invoicing .
To resolve that issue you need to do below steps.
Path -> account payable -> Vendor invoice -> Pending vendor invoice
Select the vendor invoice then you can fill the information and try to post but if there is incomplete data in invoice form and not posted than it can be stored in invoice history.
Path of invoice history form is as below.
Path -> account payable -> inquiries ->Invoice history and matching details
Filter the purchase order and delete it than you can open vendor invoice and post without any problem.