Video podcasts not able to be played?

[skybolt]

I have a 32 gig iPod Touch with the recent update -- not jailbroken or hacked in any way. I subscribe to several video podcasts. I am now getting the message for some of the more recent episodes of certain ones that they "cannot be played on this iPod". They are all MPEG-4 files, downloaded automatically from iTunes via subscription. I have tried deleting the episodes, unsubscribing and re-subscribing, but nothing has helped. Why can't they be played on my iPod?

Thanks in advance!