Iphoto export unknown error

OK - some other possible causes I am aware of, generally coming from Photos not being able to locate the original file:

• You are using iCloud photos with optimise mac storage switched on (though this doesn't usually impact exports.
• You are using a referenced library (image files not stored inside the library), and photos has lost the link to the original on you disk.
• You have your library stored on an external drive with an incompatible format (It must be APFS or MacOS extened (journaled) with the "ignore ownership" checkbox ticked.
• Some files are now an incompatible format, or have an incompatible colour profile attached.

I would still try "revert to original" even if they are not edited files - if it is available.

Hi

Are you actually using iPhoto as stated, or Photos. The reason I ask is you are in the forum for the Photos app, and Iphoto has been discontinued and undeveloped for some years.

Are all photos failing to export - or only some of them. It sounds (from the error) that most are exporting and there is only 1 or a few that are failing. Are you able to identify the ones that won't export?

If you can, the most likely cause is they have been edited in a different app (eg iPhoto or Aperture, and those edits are not compatible with the Photos app. In which case, the solution is to revert edits to original for those images (obviously in this case you also lose the edits.)