The Standard Bank Web site went down briefly yesterday morning, leaving its online banking services unavailable.
The bank says the problem lasted around 30 minutes and described the disruption as "minimal".
Spokesperson Ross Linstrom says all users encountered the same error. "When customers tried logging onto the Web site, they received a message that said the site is currently down and if they wanted to use Internet banking they would be re-directed from the landing page," he explains.
Linstrom notes the cause of the incident is under investigation and the bank apologised to customers.
Frustrated users turned to Twitter, with one person asking: "Is the Standard Bank Web site having a blue Monday?"
"What's going on with Standard Bank?" asked another user.
Some lambasted the bank for inaccessible services, with one tweeting: "What a stuff up - Standard Bank wants its users to register for UCount rewards, but its Web site won't actually let them!"
Yesterday's problem follows a technical glitch which brought down the bank's local network at the end of last month. During that time, customers were unable to carry out electronic funds transfers, draw money from ATMs, or use their credit and debit cards for payments.
Another of SA's big four banks, First National Bank (FNB), experienced a system-wide failure in March 2012 when a power outage in Randburg disrupted ATM services, credit card terminals and online banking.
FNB's backup power supply failed to kick in when its battery was blown, resulting in widespread transaction problems for customers. The bank then resorted to its alternate data centre shortly after, in an effort to restore systems to full capacity.