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Unable to open Photo Library after migrating to new iMac

I used Migration Assistant and a Time Machine back-up to move all of my content onto a newly purchased iMac. The Time Machine backup was from my older iMac running Mojave and my content was installed on the new iMac running Catalina. There were no error messages when Migration Assistant was done. Then I updated the OS to Ventura 13.2.1. All seemed fine. However when I eventually tried to open Photos I received the message that

"An error occurred while migrating the photo library"


Although I use iCloud generally, I did not have iCloud activated to back up Photos since my Photo Library is so large (260 GB). I rather relied on the Time Machine back-up on the external drive.


Quit and relaunch Photos did not fix the error. I also tried repairing the library by holding option-command while launching Photos, and this did not work. Restarting in Safe Mode did not get me anywhere.


Now I am trying to use Time Machine to restore the Photos Library from a previous version, but it has been stuck on Preparing to copy "Photos Library" for 24-h. Force quit does not indicate that any open app is not responding, so I did not force relaunch any application. The external HD is connected to the iMac with a thunderbolt 2 cable. How long should I expect this to take? Will it keep preparing when the iMac goes to sleep?


Photos does open on the old iMac (Mojave), although the size of the Photos Library is 230 GB (not 260 GB as on the Time Machine copy?). If I can't restore with Time Machine, would it be advisable to connect the old iMac to the new one directly and manually copy over the Photos Library?

iMac (2017 – 2020)

Posted on May 4, 2023 11:12 PM

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Question marked as Top-ranking reply

Posted on May 5, 2023 12:53 AM

Yes, I would copy the library directly from your old mac to the new mac.


But before you do that, check, if the library on your old Mojave Mac contains items, that a new Mac with macOS 10.15 Catalina or later can no longer process. You should remove older items in a legacy format from the Photos Library and convert them to a more compatible format, before you transfer the library to your new Mac. If there are incompatible videos or image files in your library, Photos can hang when trying to upgrade the library.


I would first check the videos. Are there any videos, that are not showing the codec HEVC or H.264 in the Info? These videos may need to be converted .

To check your videos:

  • Export all videos from the Photos Library on the old mac with "File > Export > Export unmodified original".
  • Create a new, empty Photos Library. Then import the videos in small groups tothe new library. Any video, that is giving an error message will need converting to a new format.

To check your library for image files in a legacy format use a smart album searching for the filename extension as described here: How to Weed out Legacy Media in Photos for Mac - Apple Community

I have removed all PDF files, BMP files, PICT files, also many TIFFs with color sync profiles, that are no longer supported. If you previously have used Aperture, there might be Audio files in your library, that also need removal.

You can do this by creating a new, empty Photos Library on your old Mac. And did you use third-party apps to turn video clips into Live Photos? Many of these custom Live Photos caused Photos to hang on the newer system versions.


Similar questions

3 replies
Question marked as Top-ranking reply

May 5, 2023 12:53 AM in response to salinaser

Yes, I would copy the library directly from your old mac to the new mac.


But before you do that, check, if the library on your old Mojave Mac contains items, that a new Mac with macOS 10.15 Catalina or later can no longer process. You should remove older items in a legacy format from the Photos Library and convert them to a more compatible format, before you transfer the library to your new Mac. If there are incompatible videos or image files in your library, Photos can hang when trying to upgrade the library.


I would first check the videos. Are there any videos, that are not showing the codec HEVC or H.264 in the Info? These videos may need to be converted .

To check your videos:

  • Export all videos from the Photos Library on the old mac with "File > Export > Export unmodified original".
  • Create a new, empty Photos Library. Then import the videos in small groups tothe new library. Any video, that is giving an error message will need converting to a new format.

To check your library for image files in a legacy format use a smart album searching for the filename extension as described here: How to Weed out Legacy Media in Photos for Mac - Apple Community

I have removed all PDF files, BMP files, PICT files, also many TIFFs with color sync profiles, that are no longer supported. If you previously have used Aperture, there might be Audio files in your library, that also need removal.

You can do this by creating a new, empty Photos Library on your old Mac. And did you use third-party apps to turn video clips into Live Photos? Many of these custom Live Photos caused Photos to hang on the newer system versions.


May 5, 2023 10:22 AM in response to léonie

Thanks Léonie. Indeed my Photos Library does include a lot of legacy formats since I originally imported a lot of content from iPhoto. I hope there's a way to convert all of this media into a compatable format so I don't lose a lot of these memories, but this is also going to be a tremendous amount of work that I'm not looking forward to. The advantage of using Apple products has always been that they just worked with minimal need for work arounds, but that doesn't seem to be the case with this current version of Photos. Is there an alternative to Photos that I could use to avoid this hassle?

May 6, 2023 1:20 AM in response to salinaser

Try to do the conversion on your old mac, if possible. When Apple switched the hardware from Intel to Apple Silicon, the system has been cleaned up and completely rewritten, to profit from the new hardware features, resulting in a smaller and faster system. Old 32-bit code from the old iLife times has been removed from the system, including some frameworks for legacy video and image codecs. These old frameworks are still available on macOS 10.14 Mojave. While I still have been running Mojave, I received warnings, whenever I have opened an old video that needed converting. If you skipped Mojave, you may not have received the hints to to convert your legacy media files before upgrading to the 64-bit only system versions.


On your new Mac you will need third-party apps to deal with the legacy media files. You need to clean the library up as soon as possible, because the legacy media may be blocking the background processes from analyzing the library.


Unable to open Photo Library after migrating to new iMac

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