I am kind of wondering why you are using a newer version of Plotmaker with your 8.1 ArchiCAD. Plotmaker 3.1 is the version that should install with AC 8.1. I just tried importing a saved view and a PMK file from an 8.1 PLN file I have and it seemed to work OK. However when it imported the saved view it may have been opening the file in AC 9. I could not tell.
It is simple to make a PMK. As soon as you have a plan or other view that is ready to publish just save it as a PMK file. Name it appropriately and put in a place you can find it from Plotmaker. When you open plotmaker just import the PMK file and place it in the sheet as you would any other view. The PMK file does not update automatically. When you make changes in ArchiCAD you will need to resave it overtop of the original PMK and then update it in Plotmaker. Hope this helps.
Perhaps someone else knows why you are getting this error message.
Gerald Hoffman
“The simplification of anything is always sensational” GKC
Archicad 4.55 - 27-6000 USA
2019 MacBook Pro-macOS 15.0 (64GB w/ AMD Radeon Pro 5600M GPU)