Make sure you have Install OS X El Capitan.app in your Application Folder; Select 'On an external drive' on the main MCPF window. Then, choose the disk you want to install the El Capitan installer on. Click install and prompt your password. Boot the computer you want to install El Capitan on with 'alt' held and select your USB drive. As explained here, OS X 10.11 'El Capitan' fails to install because it is too old (the technical reason being that the signing certificate is no longer valid). But you can trick the OS X installer into thinking that it is 2017 and it will happily run without any errors. How to trick the OS X installer.

El Capitan Cannot Be Installed On This Computer Windows 10

Dear Friends,

I am unable to install OS X El Capitan on my MacBook Pro running 10.6.8. I downloaded the OS X El Capitan from App Store and when I follow the installation instructions, I get this error 'This disk cannot be used to start up your computer'.

I referenced the details mentioned here: https://support.apple.com/en-us/HT203482 (Installer reports 'OS X could not be installed on your computer' or 'This disk cannot be used to start up your computer'), and the problem I am having is that I don't have a Partition on my hard disk. Unfortunately, I do not have a 'startup disk' either and thus I am not sure how to go about installing OS X El Capitan at this time. The instructions says 'If possible, back up and reformat the target disk before installing'.

I do have External Hard disk that I can use to create a backup using Time Machine, but I don't know what to do after that. Should I also copy the OS X El Capitan installation file that currently exists on my Mac Internal Hard Drive on the External Hard Disk? What should I do after I create backup on external hard drive? I have lot of data and software on my Mac and don't want to lose them all in the process of formatting the internal hard drive.

I am complete n00b with the upgrade and need assistance.

Many thanks!!!

MacBook Pro, Mac OS X (10.6.8)

El Capitan Cannot Be Installed On This Computer Without

Posted on May 19, 2016 8:52 PM