Hi, I had this problem with a 5 minute video I took that I was trying to upload to my old Mac Mini. I used the editing program in my actual camera to edit the video in half (delete the last half of the video) and instead of overwriting the clip, I made it a new file. Then I went back to the ORIGINAL clip and deleted the first half of the clip, making sure to have a little bit of overlap in between the two clips where they were supposed to match up.
They then imported fine and I just pasted them back together in iMovie. Depending on how long your clip is, you could probably clip it into thirds, quarters or whatever this way. Your camera may even have a way of splitting the clip up before importing it rather than having to make new copies of different parts of the film.
There may be a better way to do this, but I am very new and had no other equipment at that point. Also, I see you have had no responses yet, so I thought I'd throw that in there!