MacOS Monterey 12.6.2 – Failed to prepare the software update – A solution

Failed to prepare the software update. Please try again. An error occurred while downloading the selected updates. Please check your internet connection and try again.
Failure Dialog

My work Intel-based MacBook Pro refused to complete the required MacOS Monterey 12.6.2 security update. We tried everything, including:

  • Attempting the update while in Safe Mode
  • Attempting to use Recovery Mode
  • Multiple wired and wireless connections, including the hotspot from my work phone
  • Resetting the NVRAM
  • Performing a dscacheutil -flushcache
  • Creating a new admin-level account and trying the update from there

And on and on. Nothing worked until we did the following:

  1. Followed these instructions to create a bootable copy of 12.6.2 on a USB drive
  2. Rebooted the Mac into recovery mode (Option+Command+R during startup)
  3. From the menu, opened Startup Security Utility and set Secure Boot to “Medium Security”, and Allowed Boot Media to “Allow booting from external or removable media” (remember what your original setting were!)
  4. Rebooted the Mac, holding down the Control key so I could select the boot media. Selected the USB drive 12.6.2 installer created in step 1
  5. After it was complete, rebooted the Mac in recovery mode again
  6. Went back into the Startup Security Utility.  Changed Allowed Boot Media and Secure Boot back to their original settings.  You have to change them in this order because when you change the Secure Boot setting, it will want you to select your startup disk and will want to reboot right then

This look a lot of back-and -forth and several days to figure out, so I’m posting this here for the next person who runs into this. Hopefully this helps you out!

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