A Chicago festival to celebrate one year of the smartphone game Pokemon Go has been blighted by technical issues, organisers admit.
Festival attendees complained that they were unable to catch Pokemon and blocked from logging into the mobile game at all, the local Chicago Tribune newspaper reported.
The problems were magnified by hours-long queues to get into the festival location, as thousands descended on Chicago's Grant Park, the Tribune said.
In a statement on Saturday, organisers admitted that "a large number of players" experienced technical issues, and promised they would offer full refunds for all participants.
"From everyone at Niantic, we apologise to all of the Trainers who came out to Pokemon GO Fest today," the statement said.
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"Although we were able to solve many of the technical issues, we were not able to offer every attendee a great experience."
The game, which rose to prominence around the world in July 2016, works by superimposing computer-generated characters on real places when they are viewed through a mobile phone camera.
