The Central Bank has called the delay in resolving Ulster Bank's technical difficulties "unacceptable".
The bank said it has begun its own investigation into the June 19 IT glitch, which caused a huge backlog in transactions.
Central Bank officials appeared before the Oireachtas Finance Committee today to discuss the ongoing crisis at Ulster Bank.
Director of consumer protection Bernard Sheridan said the failure to restore normal service in a reasonable timeframe was "inexcusable".
"the contingency planning at RBS and Ulster Bank has self-evidently been appalling," he said. "the approach to customer communication has at times been exasperating."