I figured out a fix (not sure it's the best fix) but...
I changed the 14th line from
"With SlideShowWindows(1).View"
to
"With oPres.SlideShowWindow.View"

I'm not exactly sure why this original part at the top doesn't suffice in making it PPT specific:
"Set oPres = Presentations("X.pptm")
With oPres.SlideShowSettings"

 but it's working now : )