I have received this installation error attempting to upgrade from MacOS 26.4 beta 2 to beta 3 on my Intel 2020 27” iMac, and now trying to install beta 4 from beta 3 on my M1 Max MBP. I have seen from a sprinkling of post that some others have had the same issue. I was able to successfully perform the 2 to 3 upgrade on the iMac in safe boot, suggesting possible compatible, third-party app. But that did not work for beta 4 on either device. I have submitted feedback for each episode. Any others have this issue? Unusual for Apple, I have never had any issues installing beta software before.
MacOS 26.4 beta “Failed to prepare software update”
I am reciving the same issue on my m1 pro (MK183LL/A).
Thanks for the post. This is extremely interesting, but I'm sure is frustrating as well.
Are you able to complete the installation if you boot to safe mode?
It seems it is almost certainly a corrupted OTA (Over-The-Air) delta update file cached on your system?
The process terminates with "Failed to prepare the software update" or "An error occurred while downloading the selected updates.”?
When a beta update fails halfway or downloads a corrupted delta package, macOS will continuously try to use that broken file every time you hit "Update," resulting in the same error.
Can I ask you both to please create a bug for this issue?
Once you open the bug report, please post the FB number here for my reference.
If you have any questions about filing a bug report, take a look at Bug Reporting: How and Why?
Thanks!!
Albert Pascual Worldwide Developer Relations.
Thanks for reply, Albert. Interestingly, installation of MacOS 24.6 beta 4 was successful in safe mode on both my Intel iMac and my M1 Max MBP the second time I tried (a day later). Every time I attempted an upgrade, the Mac appeared to re-download the full OS file so not sure a corrupted cached file would explain it; also the bug presented itself on two systens with different processors. I wonder if Apple fixed a bug in the installer overnight. I did post the issue in the Developer Feedback app, and got a "request for more information", asking if I was able to install in safe mode (when I had already said that I was not). In any case, all good now. :)
I’ve had exactly the same problem on both a m3 Studio and a MacBook Air. If I go to recovery mode, reinstalling the beta seem to successfully solve the problem. The problem occurs after the beta update has completed and the verification phase starts. It sits at 5 minutes for about 5 minutes and then fails. This is happening consisteltly.
I have the same issue on my Macbook Pro M4 I tried the update in safe mode without success. Very frustrating and the first update failure in over 10 years.