I have a MacBook Pro (Retina, 15-inch, Mid 2014) running High Sierra. It works just fine. I want to create a dual-boot situation where I can run Snow Leopard from a partitioned external drive when I choose (I want to use my old Adobe applications that won't run on Sierra). I own the original Snow Leopard install disk. When I load the disk into my macbook and attempt to install the old OS on the external drive, I get a message pop up that reads: "You can’t use this version of the application “Install Mac OS X.app” with this version of macOS. You have “Install Mac OS X.app” 23.1." I hit OK and can't go any further with the install. I've tried booting directly from the disk and immediately I get a multi-language screen (similar to Windows' blue screen of death) that tells me I need to restart the computer by holding down the power button. When I do it just restarts into the normal High Sierra OS. I've tried safe boot with no luck also. I don't know what else to do, and I don't know anyone who has an older mac I can use either. Is there ANY possible way I can install my copy of Snow Leopard onto my external drive using my High Sierra macbook?