Why do some of my .MOV videos sync to iPod touch, but others don't?

I have a photo folder that contains some videos in the "Pictures" folder on my computer. The other day, I copied some of those photos and videos into another folder withing Pictures. That entire new folder and its contents copied to my iPod when synced with iTunes. Last night, I tried to copy the entire original folder to my iPod in the same way, but only the all the photos and the few videos I had transferred the first time copied.

All of the videos are .MOV so why would some sync and not others?