After configuring LiveUpdate Administrator (LUA) with a production distribution center and download / distribution schedules, distribution will fail to run if the download schedule is set to "Must Test" and there is no Test distribution center configured. The error message is "No new updates found during execution of schedule".
With no Test distribution center, definitions have nowhere to be published. They cannot be pushed to Production distribution centers until they are manually set to Pass state.
Either configure a Test distribution center, and manually "pass" content on the Manage Updates page, or change the download task from "Must Test" to "Skip Test"