Apple TV: No access to TV programmes in media library since last ATV update

Since the last update my Apple TV 2nd generation can no longer access my TV programmes in the media library. ATV prompts me with "Could not connect to xy's Mediathek (media library)". Make sure the computer os on the same network as your Apple TV, the iTunes version is up to date and iTunes is running."

If I try to airplay a programme from the iMac to ATV, the system prompts freely translated "There was a mistake in connecting with the airplay device "AppleTV". There was a timeout with the network connectivity. Please make sure, that the airplay device is running and that the network settings are correct and try again".

iMac, itunes and ATV have had the most recent software updates. iMac and ATV are in the same network, ATV shows the network signal to be 100 %, access from ATV to my music library runs smoothly, music airplay from iPhone and iMac to ATV works well. ATV has access to the iTunes shop to rent/buy movies, to my photostream, flickr accout, internet radio, etc.

I deactivated and reactivated the homesharing within ATV and iTunes. I restarted, reset and restored to factory settings including the complete process of reconfiguring access to my WiFi network and iTunes. With no effect. So, I'm out of other options to try but really would like to have access to my TV programmes again.

Any ideas? 😕