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

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

November 14, 2026 at 9:40 pm #12778
Barbara White
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.

Mac mini M4 Pro (48GB) | Studio Display | HHKB Professional Hybrid | Brooklyn, NY
Apple Certified Support Professional (ACSP) | Computer Science & Machine Learning Student