A problem with the ticket application website meant customers with a Visa credit or debit card with an expiry date of August 2011 or earlier were unable to apply for tickets.
From Monday 21 March, the website will accept ticket applications from cardholders with an expiry date of May 2011 and later. Cardholders with an April 2011 expiry date will have to wait for a replacement card to arrive before applying before the 26 April deadline because the card must be valid when payments are processed later in the year.
"It is important to stress again that tickets are not issued on a first-come, first-served basis and any ticket registration taking place by 26 April 2011 will have an equal chance of success in the ballot," said Visa Europe in a statement.
Visa is the only way to pay online for the 6.6 million Olympic tickets. Visa Europe apologised for the inconvenience some cardholders had experienced.
Some security firms also warn of fake Olympic tickets. Antivirus software provider ESET warns of a flurry of London 2012 scams after tickets went on sale this week, advising customers to check the legitimacy of sellers, delete unauthentic emails and be careful of malicious links posted on social networking sites.
Quinton Watts, vice president of marketing ESET UK, said customers should avoid internet auction sites and ensure antivirus software is installed and up to date.