Rail passengers were unable to collect pre-paid tickets from machines at stations across the country on Tuesday morning due to a fault.
A number of operators experienced problems with the system, including East Midlands Trains, Greater Anglia, ScotRail, Southeastern, Southern and Stansted Express.
Industry body the Rail Delivery Group (RDG) said the issue was resolved at around 10am.
Photographs showing the button to collect tickets being greyed out were posted by customers on social media.
One passenger wrote on Twitter that the issue affected every machine at London Liverpool Street station, which is the third busiest in Britain.
He said he had to buy another ticket as “I didn’t have time to wait”.
A spokesman for the RDG said the problem was caused by computer servers failing to communicate with one type of ticket machine.
East Midlands Trains advised customers to “board their services using booking confirmation emails”.
Passengers who had not pre-booked were still able to buy tickets from machines.