I am one of the student of Mapex training institution currently taking the course of Domestic fares and ticketing.Well from what I've learnt ,Air Niugini is a world standard organization that provides the best and quality services both locally and internationally through bigger and better fleets that is faster,e efficient and has alot of payload and more comfortable that attracts foreigners and citizens in Papua New Guineans as well..
I did finally get it to work - but i still think it is ridiculous that i have to pay for seat selection, but don't actually get to select my seats.
If you get the runtime error just start the process over and at the seat selection stage, just continue - dont change the selection. then when you reach the end you will see the boarding passes.
I did also get charged a spoilage fee for some reason, i dont think it actually went through.