There are several possible reasons why you are seeing this error message. And most of them mean, that there is a problem with the items in your Photos Library or lack of storage on your Mac or your iCloud connection. Taken at face-value, the error message means, that Photos cannot open the image or video for editing because it cannot access the original image file, cannot process it, or cannot replicate the adjustments. Tony has already mentioned the most frequent reasons. Just to add a bit of background information.
- Dating back to 2015, right after the migration from iPhoto or Aperture to Photos you may be seeing this error message, when you try to add adjustments to a photo or video, that has been edited in aperture or iPhoto. As Photos cannot replicate the adjustments applied by Aperture or iPhoto, we have to revert the photos to the original, before we can edit them further in Photos.
- More complicated, if we are syncing the library with iCloud between devices and are adding adjustments with Photos on a device with a different system version, we may have to revert the image, video, or Life Photo to the original version, before we can adjust it. Also, if the RAW support has changed between system versions.
- If the photos or videos have been imported by an older version of Photos (or Aperture or iPhoto), it may be in a format, that is no longer supported by your current system version. The coded or the color sync profile may be unreadable, because they may no longer be supported by the current system version. Then you should try to find and weed out these files and convert them to a more compatible format. This should have been done before upgrading to Big Sur, on a system version that still could handle these formats.
- You need to have the file ownership of the items in your Photos Library. The local copy of your Photos Library should be in your Pictures folder or on a volume prepared as described here: Move your Photos library to save space on your Mac - Apple Support
- A few days ago a user posted that this error message is also appearing, when Photos cannot download the edited version from iCloud. If you are using iCloud Photos, check the following:
- You need a reliable Wi-Fi connection, not a Personal Hotspot.
- You must not have third party security software (antivirus software, firewall) intercepting the connection to Apple's cloud servers.
- Your iCloud account must be working properly (payment method, enough subscribed storage available, no problems with the AppleID) - you can check this by trying to purchase a free item from the AppStore.
- You must have plenty of free storage on your Mac, so iCloud can download the adjusted versions from iCloud. Ensure that you have at least 10GB of free, unused storage on your system volume
axelnelson wrote:
Maybe it's because I feel like photo libraries might become the treasured archives referred to by generations of descendants, rather than boxes of musty ones in the garage, but it seems like an almost sacred duty for apple to make sure that their software and the files they create won't be randomly and inexplicably corrupted in their iCloud service. Of course I know that transmission entails some risk, but how much risk should apple be okay with?
Apple is keeping the files we store in iCloud safe, and backing them up, also checking for transmission errors. But iCloud is storing the current moment for us. iCloud is always syncing the local libraries with iCloud. When we work our cloud documents on our Mac and modify them, they will be modified in iCloud as well. The items in iCloud are our working set, and we need to make proper backups of our iCloud data, as iCloud does not offer an archival backup, accessible to the users. We cannot revert to a previous state of the iCloud Photos Library, there is only the recently Deleted album to get deleted items back. I am using Time Machine to have a long history of my Photos Library.
The transition from iPhoto to/Aperture to Photos for Mac and also from Mojave to Catalina deprecated many image formats and video formats. if you have not done so, check your library for legacy media: How to Weed out Legacy Media in Photos for Mac - Apple Community
For example, I had many QuickTime videos in my library, that needed converting to H.264 or HEVC, or PDFs, that needed converting.
