There's a network fault on Virgin's network at the moment which impacts on several TiVo features, including Catch Up & On Demand. This same fault also affects the TV Anywhere service.
Fortunately, the fault doesn't (or rather, shouldn't) affect recordings and playback of those recordings.
US TiVo ad - caution, contains explicit cord cutting! - http://feeds.feedburner.com/VirginMediaHighDefinition