Lloyds TSB has stated that the duplicate transactions problem that affected 200,000 customers this week related to a "systems error".
Alex Kwiatkowski, principal analyst at Ovum, who previously worked as a manager in the transaction banking division of Lloyds TSB, said there could be a number of causes.
By submitting your personal information, you agree that TechTarget and its partners may contact you regarding relevant content, products and special offers.
"As with all payment issues, this has been put down to a typical technical glitch in the system. The level of inconvenience is incredibly large."
"It could be down to operator errors, a human error or a hardware failure, or a software bug that has somehow corrupted the disk. Due to the volume of transactions, the payment processing handling would normally be very robust, which is why these events are fairly rare occurrences. It'll be one to keep an eye on to see if any more happen and a pattern emerges," he said.
Kwiatkowski added he would be surprised if it was a programming or date-related issue.
"From the evidence, it's unfortunate timing to when it occurred. The New Year's period is not a normal business working day. This could have influenced the ability for a fast resolution to be found as support staff were on holiday."
Kwiatkowski said the failure was an embarrassment for the long-running joint venture between Lloyds TSB and First Data.
"The attraction of using a third-party [for payment processing] you look for robustness. The minute you have an outage, it requires rapid resolution to make sure it doesn't happen twice."
Kwiatkowski is uncertain if this points to a industry-wide problem in the way payments are processed. "We've seen more examples of payment system problems in the past 12 months. It does highlight the technological complexity. Hawkish scrutiny of the technology needs to be maintained.
First Data told Computer Weekly it was unable to elaborate on Lloyds TSB's statement but said it was conducting an investigation following the error.