Not all iTunes video can be transferred to iPod, If the video resolution or video bit rate beyond iPod limitation, you can't upload them to iPod. For example, some iTunes purchased movie are High definition movie, the resolution is too high to play on iPod Nano, but you can highlight the problem video in iTunes and choose Create iPod or iPhone version from the Advanced drop down menu. When the conversion process has completed, sync the new version to your iPod. If you need details, here is a guide about how to transfer video/dvd to iPod. Hope it helps. Contact me if you have any other question.