The organizers of the U.K. edition of the Sonisphere festival have confirmed the cancelation of this year's event, which was due to take place July 6-8 at Knebworth House in Hertfordshire.The news first broke online last night when headliners QUEEN posted a message on their web site that their much-anticipated performance with "American Idol" alum Adam Lambert was being called off. By yesterday afternoon, however, all mention of the Knebworth show had disappeared from QUEEN's web site. Aside from QUEEN and Lambert's performance, the festival's bill also included KISS — who has also performed with Lambert during the "Idol" Season 8 finale — INCUBUS, THE DARKNESS and EVANESCENCE. Sonisphere was reportedly struggling to sell tickets for this year's edition of the festival, despite being one of the U.K.'s few remaining true rock events. Commented the organizers: "It is with very heavy hearts and much regret that we announce the cancellation of Sonisphere Knebworth 2012. "Putting the festival together in what is proving to be a very challenging year was more difficult than we anticipated and we have spent the last few months fighting hard to keep Sonisphere in the calendar. Unfortunately circumstances have dictated that we would be unable to run the festival to a standard that both the artists and that Sonisphere's audience would rightly expect. "We want to express our deepest regrets to the artists and to thank all the staff, suppliers and contractors who worked so hard with us to try and pull off what has proven to be an impossible task and we know how much they share in our disappointment. We also want to send a huge thanks to the Sonisphere fans who stuck by us and we are so sorry that we can't fulfil what we set out to do. "Ticket holders will automatically receive a full refund direct from their ticket agents."