Organisers of the Edinburgh Fringe have been lambasted for poor communication and for causing “needless frustration” among performers, the public and promoters after a new online booking system broke down, leaving thousands of customers without printed tickets.

Last night the Fringe Office, after suspending telephone and over-the-counter sales for two days, was still unable to confirm that any official tickets would be sent out to customers.

Instead, a variety of contingency plans, some requiring advance ticket-holders' names to be checked against lists of purchasers, are being drawn up with the co-operation of all 247 Fringe venues. This posed a “potential nightmare” for front-of-house staff, one venue operator said.

Already 150,000 “tickets” have been bought by thousands of customers, though none has been printed and issued by the Fringe box office, which is the central booking point for the 2,088 shows. Officials emphasised that tickets will “probably” be sent out from today for the first shows, and arrangements for clearing the backlog of sales are in place. Further delay will almost inevitably affect how ticket-holders gain access to theatres.

Amid signs of crisis at the Fringe Society, Jon Morgan, its director, said that festival-goers could still book on-line. Though printed tickets may not be issued, customers would gain access to the shows of their choice, at the time of their choosing.

Mr Morgan, who was appointed director last year, said: “We are absolutely clear that the Fringe will run as planned and we would encourage everyone to continue buying tickets and checking for updates and advice on the edfringe.com website.”

Promoters and performers were all united in insisting that their shows would go on. However advance bookings have fallen by 10,000 as confusion has spread among the local audience which forms the core of sales in the early days of the festival.

Four of the best known Fringe brands are among the worst hit by the crisis: Sweet, C Venues, Universal Arts and Paradise Green. These promoters were invited to become the first fully-integrated “linking venues” in the new ticketing system, which should have been fully operational on June 9. Each one passed responsibility for ticket sales to the Fringe box office.

All four have been left without vital data about ticket purchases and are, temporarily, out of pocket, because they have been unable to process customers' credit card details. Julian Caddy, the director of Sweet, which operates performance spaces at Edinburgh College of Art and the Grassmarket, said the Fringe office had to be held to account for a “silly mess”.

He said: “We have to look at where things went wrong. People made the wrong choices and they have to be accountable. Things could have been communicated far better by the Fringe. The problem could have been avoided, if they had sat down and accepted the system was not ready,”

Ironically, salvation may come from the organisers of the Edinburgh Comedy Festival, opened earlier this year to criticism that it attacked the “spirit of the Fringe”. The comedy festival operates an online booking system called Red61. It is understood that on-line ticket sales for the four “linking venues”, Sweet, C Venues, Universal Arts and Paradise Green, will be transferred to Red61 later this week.