The Rupert Murdoch-owned media company, which charges readers to view the websites for newspapers The Times and The Sunday Times, has refused to provide technical details about the subscription platform.

However, in a promotional video for Salesforce.com on YouTube, News International CIO Paul Cheesbrough said: "[With our Apple iPad app] you log in and authenticate, all the authentication happens through quite complex back office systems that manage you as a customer, that markets offers to you, all of this we founded on SalesForce."

He added: "We've anchored our enterprise strategy around Force.com as a platform. The [Salesforce] Service Cloud holds all of our customer information, it powers our call centres and also we've got web views into that data for our customers to renew their subscriptions."

Salesforce.com has refused to comment on the technical problems at News International.

Online subscribers to The Times have taken to Twitter to alert the newspaper to the paywall problems.

Ben Bishop, a web designer, posted a message on Twitter saying: "@Times_CS I have just received an email about not being able to take payment for a subscription I cancelled last year. Mistake? #thetimes."

Bishop told Computerworld UK that he subscribed to The Times last September on a three-month trial, and cancelled a month after the trial.

"I tried to cancel during the trial but couldn't get through to their customer services. Always engaged. So I emailed them and still heard nothing back. Due to this, I ended up paying for another month before I was able to get through and cancel.

"Then, a few months later, I received a message that they sent to everyone to say that payment had gone wrong and they would attempt to retake, at which point I tweeted them. Probably a week later, I received a message to direct message them my registered email address, but have heard nothing since then," Bishop said.

Meanwhile, customers who are still paying subscribers, have also experienced problems.

For example, Simon Crisp told The Times's customer service team on Twitter on 29 February that he kept on getting an 'expired' message even though his bank account had been debited of the subscription charge.

The Times responded: "@simon_crisp It seems as though we have been unable to take payment from you, thus you do not have an active subscription."

However, Crisp disputed this, saying: "@Times_CS that's confusing, I've had two direct debits for £8.66 taken according to my bank account?"

Another Times subscriber, who did not wish to be named, has experienced a similar problem to Crisp. Although the subscriber still has access to the websites, he received an email from The Times on 28 February, entitled 'Notification of imminent payment'. His account was last debited for the subscription on 2 December and 9 January.

In the email, Beverley McIntyre, head of customer services at The Times, wrote: "We have recently identified that your January and February subscription payments have not been taken, and therefore the outstanding amounts will be taken from your account within the next seven days.

"Unfortunately, this means that you may see three subscription payments taken in close succession – however, moving forward your next monthly payment will be taken as normal. We hope this doesn't cause too much inconvenience, and apologise for this unforeseen billing error."

News International has declined to say when the issues will be resolved.

In a statement, Chris Duncan, director of customer management for News International, said: "We've recently made changes to our subscriptions platform to improve the service that we provide to our customers.

"We are aware of the issues caused to a small number of our subscribers during the transition, and these are being dealt with by our customer support teams."