[Plugin: Add Linked Images To Gallery] Doesn't work for some linked images

It isn’t working for an image url I used this morning. I tried an image url from another source and it worked, then I went back and tried it with the first one and it still didn’t work even though my WP post showed the photo. Are there some URLs for which it won’t work, e.g., is there URL length limit (the offending URL was very long)?