Royal Bank of Scotland has admitted a number of payments expected by customers have failed to be credited into a number of accounts.The FTSE 100 group said payments including disability living allowance and tax credits did not enter accounts, although the company said it had now identified the cause of the problem.Customers from RBS, NatWest, Coutts and Ulster Bank - all part of the same group - are understood to have been affected by the issue, for an approximate total of 600,000 transactions."We are aware of an issue with our overnight process which has resulted in some of our customers not having credits or direct debits being applied to their accounts," a spokesman for RBS said."We are working to get this resolved as quickly as possible and apologise to customers for the inconvenience caused.The group suffered a similar technical problem in 2012, when a software issue left millions of customers unable to access accounts, which led to the bank being fined £56m by regulators.RBS shares were up 0.06% to 350.50p at 09:54 on Wednesday.