Ipod touch won't download audio podcast

My second generation Ipod Touch continues to display error message that an audio podcast "cannot be played on this Ipod" even though previous podcasts from the same source and series have successfully downloaded. I tried to download three consecutive podcasts of the same series from ITunes and the first one downloaded. The second two gave me the error message. A podcast from another series also gives me the error. I have restarted the Ipod and continue to get the error.