Currently Being ModeratedJun 17, 2012 7:26 PM (in response to Pabii2)
Some podcast videos are in HD, which can be 720p or 1080p. If the ones you cannot load on the iPod are HD, they exceed the maximum resolution for videos that play on the iPod, which is 640x480.
Since these are podcast videos, you should be able to convert them. Select the video in iTunes. In the Menu Bar, under Advanced, select Create iPod or iPhone Version. This should convert and save a version of the video that can load on the iPod.
NOTE: These converted videos seem to show up in the Movies category, instead of Podcasts.
Alternately, since the conversion process can take some time, you may be able to find a version of the podcast that is "Standard Def" (not HD), and download that version.