iMovie does't recognize some of my photos

I'm trying to make a video of my art for the entire year. I just made a video from all my art for December and it worked fine. I've been making videos monthly all year - no problem.

So I made an album and included all my pieces of art (263 photos) for the year. When I go into iMovie to create my movie - I can see the entire album (well 258 of the 263 for some odd reason) but when I select all and try to move them into the movie it only allows me to include a few of the photos and when I try to include some photos individually (mostly earlier from the year) I get a little white circle with a line through it.

I checked and the photos are jpg. I tried putting iMovie into the trash (not deleting) and downloading a new version. I tried restarting my computer holding down the command, option and shift keys (as suggested in another thread). I just can't seem to get my photos into my movie.

So what should I do now?