Problem: Trying to upgrade to macOS Sierra on my MacBook pro (15-inch, Mid 2012) and I keep getting an error saying that my disk is locked. So I’m not able to select the hard disk to install the OS. Tried rebooting it just brought be me back to the macOS Utilities menu. Tried reinstalling the macOS option one more time and still got the disk is locked error.
What I tried:
– Went into disk utility and ran first aid pos the HD. – no errors and no luck
– Disk Utility again and tried to erase the disk and I got an error saying that the disk could not be unmounted. i’m sure that is related to the inability to installing Mac OS Sierra
– I tried to reboot to the old OS and when I tried to choose the startup disk I go the error: “Startup Disk could not gather enough information on the selected disk”
Shutdown my computer, powered it back on holding the Command-R combination and was brought to the older mac OS utilities menu. Went into disk utility and tried to verify disk and got the following error: “This disk needs to be repaired. Click Repair Disk” I clicked on Repair Disk and after a few minutes I got another error: “Disk Utility can’t repair this disk. Back up as many of the files as possible, reformat the disk and restore your backed-up files.”
Thankfully I don’t need to backup any files so I chose to erase the disk and reinstall. After erasing the hard drive I had to go into internet recovery and had to install OS X Lion first and then upgrade to mac OS Sierra.