hi,
i wanted to contribute to this because i spent a day studying all the forum answers and had a lot of mind blown situation. So
I would like to sum up. In general i think that all these actions are necessary to solve the problem:
1. very important: upload some logo into the /images/stories/virtuemart/payment & /images/stories/virtuemart/shipment folders. Otherwiae you get this default image placeholder inside the configuration screen, that does nothing
2.make sure you have assigned logos to all parameters (vendor, shipment methods, payment methods, manufacturers )
3.connect a contact with the shopper information and add a logo to this contact
4.i came up to the point where only the Confirmed order status was producing the error, so i went to Configuration/ Order statuses and deleted the Confirmed Order Status , instead i am using the Confirmed by Shopper Order Status and i am ok with that.
5.of course i uninstalled the tcpdf and installed the new version
6.i installed the new version of allio component
hope all this helps.
i think is really annoying to have such problems on processes that are basic functionality like sending the invoice. It is not something hardcore, but ok this is a free product and after all i use it always like a cart solution and i would totally recommend it.