I recently had to erase my 2018 Mac mini and I’m now trying to upgrade to macOS Catalina 10.15.6. However, after running the installer, I keep getting the error message “An error occurred while preparing the installation. Try running this application again.”

I’m not sure why this is. I’ve ran it 4 different times, restarted, deleted and re-installed the installer for Catalina, and nothing happens. Still getting the error message. Is there any way I can fix this and get it to work? Had the same issue while trying to re-install Catalina on another machine after resetting. Not sure what to do here.

  • It’s currently 11:22 PM Wednesday August 5th where I am, has it been rolled out yet? (I’m on the East coast in the U.S.) Aug 6, 2020 at 3:23

1 Answer 1


There was a known issue with upgrading or installing the OS on Macs with a T2 chip to macOS 10.15.6. Apple have yet to acknowledge the problem but have rolled out (about 3 hours ago) a new update to the software catalog that is reported to fix the problem.

Give it another try after 0000 UTC Thursday Aug 6 as Apple has replaced a wrong installer for most T2 Macs.

  • I’m curious where this issue is known. We’re not seeing it at work, but mostly we’re focused on Mojave installs this month.
    – bmike
    Aug 6, 2020 at 0:45
  • I first heard about the problem last night my time in the #Catalina channel of the MacAdmins Slack server, That's also where I heard that Apple had fixed the problem. Aug 6, 2020 at 0:52
  • Technically, yesterday Apple pushed out a forked 10.15.6, probably due to the new iMac dropping, and it was targeted at too wide a hardware set. Then early this morning, my time, they deprecated that update and dropped one with a fixed scope. Aug 6, 2020 at 1:07
  • Thank you Tony! That could surely fork people. E.H. Is amazing, I see the posts now.
    – bmike
    Aug 6, 2020 at 1:18

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