Using the Shared folder can be a little tricky on a Mac. When you put stuff into that folder, it doesn’t automatically update the permissions so that it can, in effect, be shared to the point of letting everyone on the computer edit it. They might be able to read it, but for some things, like Scrivener projects that cannot be opened without editing them (to some small degree), the error you are getting is not unusual.
There is a checklist for fixing read-only projects, on our knowledge base. I would however recommend doing so on a copy in your actual user folder, rather than continuing to use the Shared folder like this. Not only can be a bit problematic, but nothing in there is protected from prying eyes, by definition.
Thanks so much, that’s going to save a metric ton of copy/paste! It loses the images, but it’s better than losing it all.
That shouldn’t normally happen, but some things that might cause that are using linked images originally, or using a file format that worked in Windows but not on Mac. Linking is one of the things that really cannot be easily made cross-platform compatible, given how very different addresses are between systems (never mind the path itself probably being different).
Fortunately, mass broken image links are a lot easier to fix on a Mac. On Windows you’re pretty much toast because none of the recovery or methods for fixing them were implemented. On the Mac, under some conditions you might never even noticed they were broken as it has self-healing code. In cases where that doesn’t work, broken image links are printed as regular text in the editor, which can be fixed all at once with a global search and replace, and then reloading the project.
Refer to §15.6.4, in the user manual PDF, for more detail on how the above works, starting with subheading, Links on Multiple Devices.
But, if it is a matter of incompatible image formats, there isn’t a good way around that other than going back to the originals and converting them.