After configuring LiveUpdate Administrator (LUA) with a production distribution center and download / distribution schedules, distribution task will fail to run if the download schedule is set to "Must Test" and there is no Test distribution center configured. The error message thrown is "No new updates found during execution of schedule".
With Test distribution center not configured, definitions cannot 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"