iMovie on ipad Mini export issues

Does anyone else often get the pop up saying an error has occurred or that their video does not export? I'm trying to save to my camera roll a short 15 second time lapse with a song in the background, but when I try to export the movie it looks as if nothing is working. The export bar stays completely gray for hours on end and then when I lock the device it gives me an error popup. Any solution as to how to successfuly export the movie?