I can't put a video on my iPod

When I go to my iPod I have the settings as 'Sync Movies' I have the video I want to add ticked, as well as some other videos. All the other videos go on to my 2nd generation 8gb iPod touch. It's not a question of space because I have enough left. Also, when I un-tick a video, more space appears on the bottom. But if I tick or un-tick this video it doesn't change the space I have left. Help would be appreciated!