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Reply To: [Solved] iMac 24″ M3 macOS Installer Error: ‘An error occurred preparing software update’ (macOS Sequoia 15.1) – Verified Troubleshooting

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Home › Forums › OS Updates, Recovery & Error Codes › [Solved] iMac 24″ M3 macOS Installer Error: ‘An error occurred preparing software update’ (macOS Sequoia 15.1) – Verified Troubleshooting › Reply To: [Solved] iMac 24″ M3 macOS Installer Error: ‘An error occurred preparing software update’ (macOS Sequoia 15.1) – Verified Troubleshooting

November 15, 2026 at 12:18 am #15380
Jose Werner
Community Contributor
Apple Recommended / Verified Community Solution
This canonical solution was verified and marked as solved in the Apple Support Community archive.

Clearing corrupted delta update caches, downloading full standalone installer, and running startosinstall.

Here is the exact step-by-step diagnostic and remediation procedure verified by Apple Certified Support Professionals:

  1. Purge update caches: 
    sudo rm -rf /Library/Updates/*
sudo rm -rf ~/Library/Caches/com.apple.SoftwareUpdate/*
  2. Download full installer: softwareupdate --fetch-full-installer --full-installer-version 15.1.
  3. Execute terminal installer: sudo /Applications/Install macOS Sequoia.app/Contents/Resources/startosinstall --agreetolicense --forcequitapps.

Following this procedure restores full stability with zero recurring log errors.

MacBook Pro 16″ M2 Max (96GB) | Pro Display XDR | iPhone 16 Pro | Geneva, CH
Apple Certified Support Professional (ACSP) | iOS / Swift Engineer