HSBC's online Secure ePayments application crashed again earlier this week leaving retailers unable to process card transactions for the second time in a fortnight.
The latest outage comes less than two weeks after a similar problem left customers unable to process transactions over the last weekend of March. It is thought that the platform also crashed in January, leaving merchants unable to process transactions for a day.
Furious retailers have flocked to online message boards complaining about a lack of communication from HSBC about the situation and calling for compensation.
One disgruntled customer posted an e-mail from HSBC on a discussion board yesterday evening in which the bank says the problem relates to the bank's databases.
The e-mail says HSBC had suspended the Secure ePayments service and the earliest it will be restored is Wednesday morning.
Reports of the Secure ePayments fault follow Monday's news that HSBC has lost a computer disc containing the confidential personal details of around 370,000 UK life assurance customers.
Furthermore, last Thursday the bank was slammed by Financial Union Unite for shutting down a payments processing centre in Livingstone, Scotland, leading to the loss of 164 jobs.
HSBC says the Secure ePayments service has now been restored and is live.
The settlement process for all transactions processed on 7 and 8 April has now been completed, says the bank in a statement.
HSBC says it has identified the reason for the failure and taken the necessary "corrective action" but further analysis is required before it is able to confirm the precise root cause of the problem.