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Maria Roberts

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  • November 14, 2026 at 9:19 pm in reply to: [Solved] iMac 24″ M3 encountering macOS Installer Error: ‘An error occurred preparing software update’ after update (macOS Sequoia 15.1) #12520
    Maria Roberts
    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 Air 15″ M3 (24GB) | LG UltraFine 5K | Apple Pencil Pro | Madrid, ES
    Apple Certified Support Professional (ACSP) | Product Designer & Design Systems Lead
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