Are you booking a ticket for travel via London as these still require paper tickets to access the underground?
Also, I think this is still the case, Southeastern ticket gates don’t take e-tickets. Well they weren’t doing so when I last traveled with SE late last summer. There may be other
TOCs▸ ticket gates that don’t accept e-tickets.
I too modernised to e-tickets a while back as I was fed up with the either the tickets machines being out of order at our local station or the machine not wanting to recognise the credit card I booked the tickets with.
Referencing this thread:
http://www.firstgreatwestern.info/coffeeshop/index.php?topic=27231.0Both machines are of the original ancient variety.