Can someone kindly explain how to copy a video clip onto an iPod Touch?

I've bought a few music videos from the iTunes Store and they copied onto the iPod no problem. I've since bought an episode of Beavis & Butthead, but this won't sync onto the iPod. The option 'Create iPod version' from the Advanced menu in iTunes is greyed out.

The various help pages on Apple's website mention about videos possibly being in the wrong format, but anything from the iTunes Store will be fine.

The 'report a problem' link in my email receipt from iTunes is a dead link!

Any ideas?