A planned three-day concert marking the 50th anniversary of the Woodstock music festival has been thrown into doubt after investors said they had cancelled the event, but organisers insist it's going ahead. Woodstock 50 is planned for August 16-18 at the Watkins Glen motor racing venue in upstate New York, with a line-up that included rapper Jay-Z, star singer Miley Cyrus and rockers The Killers. "The bottom line is, there is going to be a Woodstock 50th Anniversary Festival, as there must be, and it's going to be a blast," Woodstock 50 said in a statement. It has been promoted as a modern version of the August 1969 Woodstock festival, which was billed as "three days of peace and music" and is regarded as one of the pivotal moments in music history. On Monday, the festival's lead investors "decided to cancel the event." Dentsu Aegis Network, a unit of Japanese company Dentsu Inc, said they were pulling out because they felt the festival could not be produced "while also ensuring the health and safety of the artists, partners and attendees." Dentsu had a clause in its contract that gave it the option to cancel the festival, a representative of the investors said. Woodstock 50 said it would seek new investors. Michael Lang, the co-producer of the 1969 Woodstock festival and the man behind Woodstock 50, announced in March that more than 80 musical acts, including 1969 festival veterans John Fogerty, Canned Heat and Santana, would take part. Some 100,000 fans were expected to attend. But the festival ran into trouble two weeks ago when the sale date for tickets was postponed, and ticket prices have not been announced. The festival met delays in obtaining permits, arranging security, water supplies and sanitation, said a source close to the event. Capacity was reduced to around 75,000, cutting into the financial feasibility of the festival. Australian Associated Press