Message: MacOS Installation Couldn't be completed.

Safe Mode will try to repair the drive before loading, but sometimes using Disk First Aid from the Restore Partition does better... CMD+ r keys on startup.

Whew, never have I seen so many problems, & it really went downhill after...

(/Volumes/Macintosh SSD/Library/Updates/AtomicUpdates/041-31490/041-31490.Dutch.dist) did not load with error: The file doesn’t exist.

So, have they tried Disk First Aid from the Restore partition?

Can you clarify this statement???

Then he has reinstalled macOS, and with success. The iMac starts up again as it should.

Thanks, great info! :)

Updates & Upgrades have become a nightmare for many, I'm going to guess the could not update problem stemmed from Mohave trying to install itself, that has happened even on Macs that can't possibly run Mojave.

Makes me afraid to update or upgrade.

Just to be clear, nany have thought or exected the security update for High Sierra being installed when the Mac was going beyond the call of duty & was trying to install Mojave with no such input from tje user.

But many have just had inexplicable install problems, I once thought it might be a screw up on the server end.

For the problem "The main OS Installer distribution (/Volumes/DS10 SSD/Library/Updates/AtomicUpdates/041-31490/041-31490.English.dist) did not load with error: The file doesn’t exist.", I saw on my MAC this after the recent security patche update. I held down SHIFT and was able to safe boot.

I found a file installinfo.plist in /macOS Install Data/ (I think, either that or /Preboot…), there is an error in this file. Make a copy of the original and keep it safe. Then make another copy onto a place where you can edit it (I used Xcode).

Change the Payload Directory string and Software Update Distribution string. Remove /AtomicUpdates from the path. Your language will of course differ. My new strings looked like this.

/Library/Updates/041-31490

/Library/Updates//041-31490/041-31490.English.dist

Copy the file installinfo.plist back to the original place. You will need to authenticate this change.

Once I did this, I rebooted and the update finished without further problems.