Tesco's website crashed at the weekend, in spite of the supermarket investing in web cloud technology to reduce the chance of such an event.
The "double-your-vouchers" promotion, in which customers could multiply the value of their Clubcard loyalty tickets, ran throughout November but there was a rush last weekend when the promotion ended.
Huge queues resulted in-store, and customers rushed online as an alternative. This meant many thousands of Tesco customers were unable to take part in the scheme.
The online crash is seen as a potential embarrassment for the supermarket only days after it trumpeted the fact it had gone into the cloud for third party support to protect its website under heavy traffic.
The supermarket was using Akamai Dynamic Site Accelerator services to support the company's "2010 Clubcard Bonanza". An Akamai spokesperson today insisted that the crash was on "part of the network" that was "not supported" by that company.
Having looked at ISPs and "discovering that they couldn't support the kind of bandwidth Tesco demanded", the company took a different approach, Akamai said at the time the additional cloud capacity was added. The aim was to "take the load" from Tesco's infrastructure and "provide the support we needed, no matter how much traffic visited our website", said Ed Camp, head of server and storage at Tesco.com.
Early on in the Clubcard campaign, peak traffic had reached 120Mb/s, with Akamai's Dynamic Site Accelerator services in the cloud offloading 90 percent of this from Tesco's servers.
Last year, in another Clubcard promotion before Christmas, tills at around 100 Tesco stores crashed following a routine IT upgrade, with some being forced to close as a result.
Those customers who missed out on doubling their Clubcard vouchers this year are being encouraged to contact Tesco customer services.
Tesco said in a statement: "We experienced a huge last-minute rush over the weekend. This meant that some customers were not able to exchange their vouchers or had problems with the process, and missed the deadline of 5 December. We are doing everything we can at our customer service centres to help those customers affected."