I'm not sure where the problem originated from, but I noticed Autoblog needed an update, and all the images that had come through from the another blog had a ? error.
When I tried editing pages using my site's page builder to add images, I had the same error.
See this page as an example:
Why does the top image appear as an error, but not the bottom one? The only difference was the bottom images was added several months ago and the top image was added this morning.