The chairman of Ulster Bank owner Royal Bank of Scotland (RBS) told the lender's annual meeting that its IT systems needed to improve.
The admission comes after the taxpayer-backed bank's latest embarrassing IT glitch that saw 600,000 payments fail to go through to customers last week.
The problems affected all four of its banking brands - Ulster Bank, NatWest, RBS and private bank Coutts.
At the Edinburgh meeting, Sir Philip Hampton told shareholders: "As last week's processing delays showed, whilst we have invested heavily in rationalising and simplifying our systems and processes, we need to continue to improve overall performance."
It is another blow to the group, which has been hit by a number of IT failures in recent years.
In 2013, RBS's online service was disrupted by a denial-of-service attack.
And last November, the state-backed group was hit with a £56m fine from the Bank of England and City watchdog the Financial Conduct Authority after a computer failure in 2012 saw as many as 6.5m customers at NatWest and Ulster Bank unable to make payments for as long as three weeks.
Sir Philip said his six years at the head of the bank had been full of ups and downs, but he was sure he was leaving the lender in a stronger position.
He said: "There have been highs and lows along the way, but overall RBS has made great progress since 2009.
"It has been fundamentally rebuilt - it is now a bank that is much safer in capital strength, in structure and increasingly on behaviour."
The annual meeting also comes as the Government prepares to begin selling the taxpayers' 79% stake in the bank after Chancellor George Osborne announced the plans in his annual Mansion House speech.
He said the stake sale would begin in the coming months, but admitted the Government stands to make a loss of about £7bn if the entire stake is sold off in one go.