Hackney Weekend tickets go back on sale
More tickets for Radio 1's Hackney Weekend are being released after the ticket website struggled to cope with demand on Sunday.
Fans, who had pre-registered for the free two-day concerts, complained about receiving "access denied" messages and being unable to book tickets.
Radio 1 said the problems were caused by the "high volume of traffic after an unprecedented demand for tickets".
Another 50,000 tickets were released for the event from 16:00BST.
Jay-Z and Rihanna will headline the concerts on 23 and 24 June, which is part of the2012 Festival.
Other acts in the line-up include Leona Lewis, Example, Plan B, Florence and the Machine and Tinie Tempah.
"We're aware that some listeners experienced problems whilst trying to book tickets online for Radio 1's Hackney Weekend yesterday morning," a Radio 1 spokeswoman said.
"We apologise for the frustration this may have caused. People have now been successful at getting tickets and we're hearing from lots of happy listeners. ''
The majority of tickets have been reserved for those from Hackney and the other five Olympic boroughs.
But fans who live outside London complained that by the time they could get onto the website at 13:00, the tickets had sold out.
Shereena Grey wrote on the event'sunofficial Facebook page: "Started refreshing the page from 10:40... got a holding page for 2 hours, finally got the "buy ticket" page at 13:00 ... SOLD OUT. I hope tomorrow is not the same."
However others were successful with their orders - Nicola Alexandrou posted on Twitter: "Got tickets for Sunday at #r1hackney this morning! Can't wait to see @rihanna."