Brighton Pride has suspended a second round of ticket sales after admitting it was "struggling to cope" with the number of people people trying to buy tickets to see Britney Spears.
It was announced last week that the pop icon would bring her Las Vegas show to the UK, headlining Pride on 4 August.
Scores of unhappy fans criticised the website problems on social media.
Organisers earlier urged people to "please bear with us" while the "tech team" tried to resolve the issue.
They later announced the second release of tickets had been suspended, and apologised for the website outage.
The first round of tickets for the event, which describes itself as the biggest pride festival in the UK, went on sale on 17 January.
Many people took to social media complaining the website had crashed, and all the "early-bird" tickets had been sold within minutes.
Last week organisers tweeted they were "thrilled" to announced "legendary" Spears would headline the three-day festival in Preston Park.
The second phase of tickets was released at 08:00 GMT, with the website crashing again.
Brighton Pride tweeted: "2nd release Pride Festival tickets went on sale at 8am today. Despite running 16 servers and a dedicated database server our website is still struggling to cope. Please bear with us while out tech team try and resolve the issue."
But fans took to social media to share their frustrations at failing to get the tickets:
@PrideBrighton I’ve been trying to get on for over 2 and a half hours, are there still tickets available or should I give up and actually do work?— Annabel Armstrong (@AnnabelEvelyn) February 1, 2018
What about those of us who are going to have to leave for work soon but have been refreshing for the last half an hour? Are we going to miss out? Seems very unfair!!— Kat Brown (@kat_brown22) February 1, 2018
Brighton Pride are irresponsible for announcing that Britney Spears would be participating in this year's event BEFORE tickets were available. Inevitable that her fans would rush to buy them.👎— Sundancin' Paul (@Sundancer_UK) February 1, 2018
Last year about 300,000 people attended the Pride parade through Brighton and Hove, with many anticipating a packed city again this year.
Crowds gathered from early in the morning as the 100 floats gathered on the seafront.
In 2017, the Pet Shop Boys headlined the event at Preston Park, which marked 50 years since the partial decriminalisation of homosexuality in England and Wales.