Sounds like you are trying to sync the HD version of the these shows you purchsaed. You should try to download the Standard Definition copy instead and sync that to your device as HD content is not compatible with your particular model iPod. See here for more information:
To prevent HD versions from being downloaded in the future head to the iTunes Store, click the Purchased link, and then select TV Shows and remove the tick mark next to Download HD when available. You should be able to download the SD version now from under this same page.