Same problem with TubeDigger - their support confirms that Channel 5 now uses additional encryption. This appears to affect content from the past couple of weeks onwards. Only time will tell whether they will retrospectively apply it to everything.
The workaround for now is to use the
Demand 5 YouTube channel. TubeDigger is able to download videos in "Rec" mode ("recording" them as they are played), so GetFLV should be able to do something similar.