"I believe I discovered what the issue is… and therefore solved my particular issue. I believe it is a (Apple) “cloud” issue. When one is trying to upload an older photo (stored on the Apple Cloud) to ViewClix it will give the Error. But, if beforehand, I load the photo on my phone – simply view it through my photos gallery, so that it loads in full resolution – I can then go back to the ViewClix app and upload said photo to the frame."
Here is a link to the Apple support article that gives more detailed directions: https://support.apple.com/en-us/HT204055#photos
- the setting "Download and Keep Originals" does not go into effect immediately and may take overnight or days to work, depending on how many pictures are in iCloud
- It may be possible force pictures to be downloaded from iCloud: https://discussions.apple.com/thread/250674373