Complaints from music fans about the Hackney Weekend website barraged social networking sites yesterday, as it struggled to cope with demand - but the BBC is hoping the process will be smoother when another 50,000 tickets go up for grabs at 4pm.

Fans who had pre-registered for the free two-day concerts on Hackney Marsh, 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”.

It was announced on Saturday Rihanna will headline the concert on Sunday June 24, which is part of the 2012 Festival, while American rapper is the headliner on Saturday.

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.”

Half the tickets are reserved for lucky Hackney residents, and there are still tickets available for Sunday out of yesterday’s 50,000 allocation for people who registered from the borough.

But fans who live outside London complained that by the time they could get onto the website at 1pm yesterday, the tickets had sold out.

Shereena Grey wrote on the event’s unofficial 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.”

There will be another 50,000 tickets made available at 4pm, half of which are reserved for Hackney residents.

Allocation will be on a first-come, first-served basis, once where you live is taken into account.

The quickest way to apply is at bbc.co.uk/radio1.

Those unable to access the internet can call 0844 873 7347. Tickets are free but there is a handling fee of �2.50.

BBC3 will screen the event for anyone who wasn’t lucky enough to bag a golden ticket so they can see how much fun they’re missing.