Thousands of people told they had a ticket for the Leeds and Reading music festivals have had them cancelled.
Red Hot Chili Peppers are among the festival's headline acts
Weekend tickets for the event sold out within hours of going on sale on Monday but some fans were subsequently told their confirmations had been withdrawn.
Organisers said purchases were dealt with so quickly that problems with over 3,000 credit cards only came to light after the confirmations had gone out.
Those affected could buy coach package tickets until 1930 GMT on Wednesday.
About 1,100 people applying for Leeds tickets were affected alongside a further 2,000 applicants for Reading tickets.
Melvin Benn, managing director of festival organiser Mean Fiddler, said: "Cards were rejected either because their numbers were inputted incorrectly or they did not have sufficient funds.
"The sad thing is they got a confirmation and then relaxed and it wasn't until the next morning they were told there was a problem, by which time the weekend tickets were gone."
Mr Benn said they had a record of these transactions and would hold back enough coach tickets to give those fans an opportunity to still go to the festival.
The Red Hot Chili Peppers, Razorlight and The Smashing Pumpkins will headline the twin events on 24-26 August.