I just downloaded the PTV
https://www.railpage.com.au/downloads?mode=download.view&id=816 and took noticed of the contents within the archive
1) Main Folder contains
"PTV_Comeng_1_1.EXE" = Installer File, to install select MSTS/TRAINS/TRAINSET folder
"PTV_Comeng_Sets_1_1.ZIP" = Con or Consists files which should go into the MSTS/TRAINS/CONSISTS folder
2) _MACOSX Folder contains
The same installer .EXE file - I would assume this installer is for a 32-bit of Windows as I tried to run it on my 64-bit computer
The same .ZIP file containing the .CON or Consists files - this zip folder doesn't seem to be valid not sure why but use the above .ZIP file to install the consists files
I wouldn't know why you are getting the error message your having with the PTV set, not unless you have a passenger activity with one of your Victorian routes you have installed and MSTS is trying to find the .ENG file to run the activity
However, there could be a possibility that you didn't download the original file above "See the above link" as the .ENG file is located within this archive
There is a reskin version which also contains more road numbers located here
https://www.railpage.com.au/downloads?mode=download.view&id=813 so I think this could be the one causing the error message you are having as one or more .CON files are looking for the metrocomeng301M.eng file from this archive
I hope this all makes some sence, as I said before I only have NSW, QLD and some VIC wagons installed in my MSTS
So I didn't have the PTV set until I just downloaded it
1) Download and install the first PTV set in the above link at the top of the page
2) Download and install the second PTV set at the bottom of the page
Not sure if it will fix the error message but it would be a fair guess that maybe you only downloaded one of the PTV set files
Let us know how you go