I have never before used autohydro. However, that looks exactly like a run file for GHS. I know the two programs have a lot in common, but I do not now what aspects or how much (there are complaints of copy-write infringement or copying or thievery or something like that from one side or the other).
Anyhow, in GHS you do enter partmaker just like you wrote. ENTER PM
Perhaps you are modifying a GHS run file and not an autohydro file. Maybe they use different syntax for that. I do not know.
One thing is that in GHS after you enter partmaker you will write your part making code. It isn't common to then run an outside program from there. Not saying you can't I just haven't seen that before. So I'd normally have the ENTER PM command within the PM file Cre8tnks.run. I'd open GHS, run PM from within GHS, write PM code, exit PM, exit GHS.
This might be completely useless to you, but just for reference I've attached a GHS PM file for a small passenger ferry. I start by opening a bare hull model (boat.gf) and then I attach some junk in PM. I define the units as metric. The margin line as 3 inches below the deck (0.076m). Shell thickness as 9.5mm (3/8"). Then I model in some rough approximations of right angle drives (RAD), define the tanks, and the spaces. At the end I have two quit commands (qu), one to quit PM and one to quit GHS.
I hope this is of some help. When in doubt dig through the manual.