Organisers of the GamerCon gaming event at the National Convention Centre have apologised to people who have had to queue for hours to get into the event.
24,000 tickets were sold for the GamerCon convention.
Many of the tickets were bought by families and many young children were in attendance.
Some had to queue outside for three hours to get into the Convention Centre and were told they could get in only when others left, as the building was full.
The Convention Centre has capacity for 9,400 people and around 12,000 tickets were sold for each day of the event which runs today and tomorrow.
GamerCon founder and event organiser Ferdi Roberts apologised saying they had miscalculated the traffic flow for the event.
He said people were not expected to spend all day at the event and that it is not unusual to sell more tickets than a venue can hold.
He said ticket holders who had not come into the Convention Centre could claim a refund through the App for the event or the GamerCon website.
Some visitors said there were long queues inside the event and said the children they had brought were disappointed.
Many families spent more than €100 on tickets and had additional expenses for travel and accommodation.