When I try to install High Sierra, I get the following message: “We could not complete your purchase. This version of macOS 10.13.3 cannot be installed on this computer.” My spec is as follows: OS X Yosemite – Version 10.10.5 MacBook Pro (13-inch, Mid 2009) Processor: 2.26 GHz Intel Core 2 Duo Memory: 8 GB 1067 MHz DDR3 Startup Disk: Macintosh SSD I also tried installing via a different method: [Downloaded the OS using a different Mac, transferred it to mine.] This also has the same result. Is the issue that my MacBook is just too old to install this OS? My Mac runs brilliantly – I have no issues with it whatsoever, EXCEPT that there is now software that I am unable to use.