Security update on Sierra high fails
Then tried to reload Sierra High from recovery, but could not find a disk to reinstall all disks greyed out in selection box including main HD, did a dick first aid everything seems fine.
MacBook
User profile for user:
Leanne_68
User level:
Community Specialist
Hello and welcome to Apple Support Communities Alex_UK_Kent,
I see that when you try to do the security updates on your Mac it keeps failing. I'd be happy to look into this with you.
Let's have you try to unmount the disk. The steps are listed in the article below.
Unmount a disk set or disk member using Disk Utility on Mac
If you go through these steps and the issue remains, you'll want to try to reinstall macOS again. The article below can help if needed.
How to reinstall macOS from macOS Recovery
Let me know how this goes.