Nearly 2,000 forged tickets to the sold-out Robbie Williams concert tomorrow have surfaced in the past five to seven weeks, according to the Garda, Ticketmaster and Croke Park officials.
The real tickets have a blue background and circular seal, while the fake tickets have an orange and purple background and oval seal.
"They look sophisticated but they're not," said Éamon O'Connor, managing director of Ticketmaster Ireland.
When concert-goers enter the concert not only is the ticket checked but a barcode on the ticket is scanned.
Mr O'Connor said Croke Park and the GAA were the only ones with the barcode encription, so not only do the tickets look different but the fakes will not be able to be scanned.
He said Ticketmaster had a pilot in which they considered making orange tickets, but that never occurred.
However, "someone could have gotten hold of that information" and mistakenly thought Ticketmaster had decided to use orange.
Garda Supt John Leahy said there was an investigation into where the tickets were coming from, but no one has been questioned or arrested in connection with the case.
He added that the tickets have only been found in Dublin.
If people have concerns about their tickets they can take them to any Ticketmaster outlet to have them checked.
Peter McKenna, Croke Park stadium director, said because the concert was sold out there were ticket forgers still trying to sell them in the last days before the concert to people willing to pay more.
"It would be a shame if people spent €100 for nothing," he said.
Mr O'Connor advises concert-goers to buy tickets only from authorised outlets.
Residents in the Croke Park area waited for tickets from early morning yesterday.
Some 800 tickets were handed out in the morning, and 800 more handed out at 7pm last night.
Mr McKenna said residents had to bring photo identification and a utility bill with their name in order to collect two tickets per household.
He said that the 1,600 tickets for residents were worth £136,000.
"I would rather see that money go to schools," Mr McKenna said. "With tickets it doesn't give community gain."
Doors will open at 5.30pm, with the first opening act set to begin at 6pm.
Robbie Williams is scheduled to take the stage at 8.45pm.
At 10.30am on Friday a traffic restriction cordon will be set up similar to match days, Mr Leahy said.
An outer traffic cordon will be put in place at 10.45pm.
Other acts set to perform in Dublin over the weekend include: The Eagles, performing on Saturday and Sunday at Lansdowne Road stadium; Guns 'n' Roses with special guest Motley Crew on Friday at RDS Arena; and Metallica on Sunday at RDS Arena.
In addition to regular trains Iarnród Éireann will be operating special trains on Galway, Mayo, Cork, Kerry and Limerick routes to deal with an expected increase in passengers over the weekend.
Student travel cards and other discount cards will not be valid on special trains.
For more details, visit www.irishrail.ie