Ticket touts are attempting to sell invalid backstage passes for Radio 1's Big Weekend concert on the internet.
Snow Patrol will play at the event on Saturday
Bids for the passes on internet auction site eBay have passed the £7,000 mark, while normal tickets for the free event were being offered for more than £100.
Organisers of the Dundee music event, which includes acts such as Pink and Keane, expressed their disappointment.
A spokeswoman for eBay said it was difficult to tell between genuine and fake bidders.
But she stressed that anyone making a bid on the site was legally bound to honour it.
The backstage passes were invalidated by Radio 1 when the problem emerged and the seller was told to remove them from the internet auction site.
The concert at Dundee's Camperdown Park on Saturday and Sunday, which will be attended by 30,000 people, was set up as a free event.
Hundreds of thousands of music fans applied to Radio 1 in the hope of success in the ticket draw.
Some people who obtained tickets advertised them for sale on eBay and bids for the now redundant backstage passes quickly shot up from £3.
However, some may have been fake bidders protesting against the selling on of the free tickets.
One bidder on the site describing themselves as "ban the touts" made several bids for between £4,000 and £7,000.
A Radio 1 spokesman said: "Obviously Radio 1 is totally against people profiting from what is a free music event.
"Unfortunately with all major ticketed events there is the chance that people will auction tickets off."
The spokesman said the problem was a difficult one to police, but added: "We've got a serious security presence at the event."
Tayside Police said there had been indications that people without tickets may head to the venue to try and listen to the music from the outside.
However the force said it would be "pointless" for those fans to turn up as they would have difficulty hearing.
Other artists featuring in the line-up are US hip-hop duo Gnarls Barkley, the first act to score a UK number one single on the strength of download sales alone, and Snow Patrol, which formed in Dundee.