MovieMaker

I have put together a 1:21 minute photo video with music. It was fairly easy, but very time consuming, and I've been working on it for awhile! The photos were scanned to an external hard drive. I disconnected the hard drive for a few minutes (I had saved the project). I  have closed the project before without any problems. Today ONE picture won't show up - shows up with an error..but it WAS there. And MovieMaker plays it! But I can't save the video to DVD until I remove that picture. It is the very first picture and I feel it needs to be in there! Why did it work before and why does it not work now...and mostly, how do I make it work??? Thanks for your help!