I'm trying to install the game on my External hard driving using the offline backup installer, however when I run it, it says the following:

"Please specify the location of part 1 and click OK

By default the files should be placed in the same folder as installer itself. Please click Browse and specify the correct path."

I've tried installing it pm where I have the original Necrovision and I get the following error message

"The file could not be located in the installer's folder. Please make sure that the file is in the correct folder, or specify its current location."

I've even tried to install it directly into the bin folder of Necrovision but I still get that error message. I've looked to see if I was missing any files but from what I can tell, nothing is missing.

Does this game/expansion have some additional DRM where I need the disc to install it? Or is there something I'm missing?

Did you really download BOTH parts of the game? They probably are both at the same location (defaults to the Downloads folder if W10). Does not really matter where as you need to manually specify the installation location in this case. It should work and I have no more ideas unless you are not allowed to install programmes on your PC.

Remember you need enough space in your Temp folder.