Hi i need program a list that start at 6 PM and finish at 6 AM.

This shows an error displayed on the next picture..

http://jsteer.dreamhosters.com/otros/Error%20Centova.JPG

How can i do it?

Scheduled playlists currently have to be scheduled within a single day. Future versions will lift that limitation but for now you'd need to create a 6pm-midnight playlist and then a separate midnight-6am playlist.