Error downloading Image/Video

My iPhoto has done this a couple of times now. I film a video, try to download it from my SD card to iPhoto and iPhoto will give me an error. My video will not show up in iMovie either. Has this been happening to you? What can I do to fix this? It just tells me "iPhoto cannot import your photos because there was a problem downloading an image.", nothing else. I mean, I could understand if there was a reason..

Thank you for taking your time to read this! I hope some of you can help.