problems making imovie out of photos

Why am I having trouble with iMovie? I'm trying to make a wedding video out of photos from the life of groom and bride. I get most of the way through, and suddenly when I try and import another photo, a previously-inserted photo appears in the project pane instead. I've tried edit>cut, delete selection, and delete entire clip. It still comes back in the same.

I went to the Apple store last week and they advised I can't make changes to the folders the image files are in after I've started the project, so I went through and numbered all the photos and organized them prior to making the movie. I haven't made any changes, yet it still makes this error. It's very frustrating.

Any ideas? The wedding's in 2 weeks!