Ticket offices couldn't issue tickets from early on until 11.45am, though they were available from vending machines and on the trains.
Here's the explanation from Northern Rail:
"At 06.30am this morning a server failure occured affecting our ticket offices across the north west. This happened at 67 stations and the problem has now been rectified. We provide our customers with alternative opportunities to purchase tickets, 25 of these stations have a Ticket Vending Machine (a self-service ticket machine), and customers also have the opportunity to purchase a ticket on board trains, and we have no reported wide spread issues with this service."