Here's what worked for me:
- I had 350 photos, and it errored out 12 times at various intervals, even after I rebooted everything.
- So I highlighted only the first 150 and they imported fine, then deleted them from phone. Then imported the next chunk, deleted from phone, etc. until all done.
It appears Apple couldn't handle the size of all of the pictures. After rebooting the devices, I got much further (almost to the end with only 24 pictures left to import) but then it errored out again, and none were imported. So, by importing in smaller chunks, it was able to handle it fine.
So, if all else fails, try that!