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Bugs Killed

Mac

My Mac says an error occurred while installing the macOS update

A macOS update or upgrade stops part way and shows an error while downloading, preparing, or installing, or says the software is damaged, could not be verified, or failed to personalize. Apple lists the checks that clear most of these, starting with free space and a stable connection.

Affects

Versions

  • macOS Tahoe 26
  • macOS Sequoia 15

Apps

  • Software Update
  • macOS installer

Hardware

  • Macs with Apple silicon
  • Macs with the Apple T2 Security Chip

What you see

  • The message says that "an error occurred while downloading, preparing, or installing"
  • The message says "the software is damaged, could not be verified, failed to personalize, or needs to be reinstalled"
  • A message says "There is not enough free space on the selected volume to upgrade the OS"
  • The install screen sits on the Apple logo with a progress bar that does not seem to move
  • A message says "macOS could not be installed on your computer"

Why it happens

Confirmed Apple says "The message might say that an error occurred while downloading, preparing, or installing", that the cause can vary and is sometimes only temporary, and lists free space, a stable internet connection, other software interfering with the installation, a damaged installer, and disk problems as the things to check. [1]

Likely A macOS upgrade needs far more free space than the download itself, so a nearly full disk is a common reason an upgrade fails part way. [2] [3]

When it shows up

The message names storage space, or the disk is nearly full

You are in this case if:

  • The message says your Mac does not have enough storage space, or that there is not enough free space on the selected volume
  • System Settings > General > Storage shows very little available
  • The install fails at the same point every time

2 fixes below

The download or preparation fails, or the installer is reported damaged, and this is the first or second attempt

You are in this case if:

  • The error mentions downloading, preparing, verifying, or personalizing
  • The Mac is on Wi-Fi that comes and goes, or on a captive network
  • The progress bar has not moved for a long time, or the screen went blank

3 fixes below

The installation fails again after the simple checks

You are in this case if:

  • The same error returns on a Mac with plenty of free space and a steady connection
  • The Mac starts up but the update will not complete, or the Mac does not start up all the way
  • A fresh installer fails the same way

3 fixes below

The steps that killed it

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Keeping it away

  • Back up the Mac before any macOS upgrade, since that is Apple's own advice before installing new software.
  • Leave well more free space than the download size before starting an upgrade, and run the install while the Mac is on power and on a steady network.

Sources

  1. If an error occurred while updating or installing macOS
    Apple Support, 2026-04-29
  2. Free up storage space on Mac
    Apple Support, 2026-07-06
  3. How to update macOS on your Mac
    Apple Support, 2026-06-01
  4. What to do if macOS won't install: Fixes for stuck macOS update
    Macworld, 2024-09-16
  5. Apple System Status
    Apple

Last verified 2026-09-14