iMovie is not processing some of my videos

Hi! First time on the discussion boards. Usually I am able to figure something out myself, and if not, a quick search online gives me the answer...but not this problem.

I have my wedding footage that I am trying to edit and compile to make a video. Original footage was captured in some format that is not compatible with quicktime; I believe its UNIX (or something). I converted all clips to mp4 and have been transferring them to iMovie so I can begin editting. Here is the issue.

There are a couple of clips that, even though they are in the proper format, will not open iMovie. All other clips that I converted opened up fine in iMovie. I selected an event, imported movie, found clip, and it optimized, processed, and generated the clips into frames. There are a couple that will not open in iMovie. It begins the process, and then nothing happens. Whats confusing is that it is in the proper mp4 format because when I open the clip in the folder that it is saved in, it plays just fine in quicktime. Also, all other clips that did transfer properly, I did the same thing to them for the entire process (converting to transferring).

I then tried opening the video in iPhoto (I was told that sometimes corrects any error with the video). It is in iPhoto, plays in iPhoto, but won't transfer to iMovie.

I restarted everything multiple times. I even took the original footage and converted it into mp4 again (thinking something happend during the original conversion).

I don't know what else to do. Hope you were able to bear with my ramblings and I hope someone knows what to do!!

Thanks so much! Look forward to any and all assistance!