How To Fix ‘An Error Occurred Preparing The Update’ (Mac M1)

Mac M1 an error occurred preparing the update

Mac M1 an error occurred preparing the update.

You’ve purchased a new Mac to take advantage of the revolutionary M1 Apple Silicon chip but are prompted with the ‘An Error Occurred Preparing The Update’ dialog box when trying to restore the computer. Is your machine stuck at the ‘Failed to personalize the software update. Please try again’ popup? This appears to be a common problem and Apple has published a support document that informs you how to fix it.

‘An Error Occurred Preparing The Update’ Causes?

This Mac M1 error is triggered when the user decides to erase/restore the computer before upgrading to macOS 11.0.1 Big Sur. The above error message is displayed while attempting to reinstall macOS.

How To Fix ‘An Error Occurred Preparing The Update’

Apple mentions two ways to fix this: with bootable installer, or using Terminal commands in macOS Recovery.

A. Create & Use Bootable Installer

To apply this troubleshooting method you need a second Mac and an external flash drive (with a minium of 12GB of storage) or SSD that you will need to erase (format). If you do, proceed as follows:

creating macOS Big Sur bootable installer in Terminal

creating macOS Big Sur bootable installer in Terminal | Source: Apple Support

  • 1.On the secondaruy Mac, download the macOS Big Sur installer. (direct link).
    Fact: The installer downloads to the Applications folder and is named ‘Install macOS Big Sur’. The installer might automatically open after you download it, quit the installation.
  • 2. Connect the external drive that you plan to use a Bootable Installer.
  • 3. Open the Terminal app (from Finder).
  • 4. Copy paste the following command string:
    Important: MyVolume is the name of the external memory device that you’re using. If it comes with a different name, replace ‘MyVolume’ with the correct label. The following command line assumes that macOS Big Sur installer is in the Applications folder:
    sudo /Applications/Install\ macOS\ Big\ –volume /Volumes/MyVolume
  • 5. Press the Return key to run the command.
  • 6. Type your admin password if prompted. Note, the Terminal windows won’t show the characters. Just make sure that you type it correctly and hit Return.
  • 7. Press Y to confirm that you want to erase the volume and hit Return.
    Tip: If Terminal alerts you that it wants to access files on a removable volume, Click OK to allow.
  • 8. When the process finishes the removable disk will be named Install macOS Big Sur. You can now quit the Terminal app and eject the external disk.
  • 9. Connect the bootable installer that you just created to the Mac that’s plagued by ‘An Error Occurred Preparing The Update’ problem.
  • 10. Power on the computer and continue to hold the power button until the startup options window is displayed.
  • 11. Select the bootable installer, from the available bootable volumes and click Continue.
  • 12. The macOS Big Sur installer opens up. Follow the on-screen instructions to complete the installation.

B. With Terminal commands

Turn your Mac On and continue to hold the power button until the startup options window is displayed:
macOS Big Sur startup options

  • 1. Select Options and click on Continue.
  • 2. Select your administrator account and enter the password.
  • 3. In the Utilities window go for Utilities -> Terminal.
  • 4. Type resetpassword in the Terminal window and hit Return.
  • 5. Click on the Reset Password window and choose Recovery Assistant -> Erase Mac in the menu bar.
  • 6. Go for Erase Mac and click Erase Mac one more time to confirm.
    Tip: your Mac will automatically restart when the process is completed.
  • 7. Choose your language when required.
    Important: If you’re prompted that the version of macOS on the selected disk needs to be reinstalled, click macOS Utilities.
  • 8. Your Mac requires an Internet connection to activate. Click on Exit to Recovery Utilities, after the activation process is completed.
  • 9. Select Safari (in the utilities window) and click Continue.
  • 10. Enter the following URL in the Safari search field: It will bring up Apple’s support document and you will need to copy the code the following Terminal command:
    cd '/Volumes/Untitled'
    mkdir -p private/tmp
    cp -R '/Install macOS Big' private/tmp
    cd 'private/tmp/Install macOS Big'
    mkdir Contents/SharedSupport
    curl -L -o Contents/SharedSupport/SharedSupport.dmg
  • 11. Click outside of the Safari window to bring Recovery to the front and go for Utilities -> Terminal.
  • 12. Paste the copied text and hit Return.
  • 13. macOS Big Sur download begins. When finished, type the following command and hit Return:
  • 14. The macOS Big Sur installer should open now. Follow the on-screen prompts to reinstall macOS 11.

Have you managed to fix the ‘An Error Occurred Preparing The Update’ problem? Which method did you use? Share your feedback using the comments section!

Related: How to fix Mac password not working in macOS Big Sur! You might be also interested in the fix for macOS Big Sur installer causing black screen on older MacBook Pro models!