Welcome to the forum Mark, you'll find the members on here are a friendly and helpful bunch 🙂 it could be a faulty motor. Can be fixed with a simple overhaul and less than £100 rather than £1500 quoted by Audi. One repairer is Autoelectron via Ebay:
http://myworld.ebay.co.uk/autoelectron
From what I hear they're very helpful and quick turnaround. Definitely worth checking out. I have no association with them. Or it could be one of the micro switches is stuck open and is preventing the system from continuing the full cycle.
Best way is to stick the manual key between the rear seat cavity and reset it manually.
move it up or down until fully close or fully open, remove the key and try with the switch, is always better with the engine running as it takes a lot of power to operate a full cycle.
Hope I've helped.
Cheers
Steve