Royal Bank of Scotland said it has resolved problems that led to customers being unable to withdraw cash from some ATM machines.
NatWest and RBS customers have been unable to withdraw cash from other than the banks' own cash machines, the bank said.
Customers have taken to Twitter to complain about the problem.
RBS' spokeswoman Nicky Harris said customers should be able to withdraw cash from RBS and NatWest ATMs, but that they are experiencing problems while using other banks' machines.
NatWest bank customers have taken to social media to complain about being unable to withdraw money from their accounts. Many have voiced their frustration on Twitter.
Umm....4 non natwest cash machines & all of them refuse to give money! Only one that worked was a natwest...problems again? @natwest_help
If you're a #NatWest customer you can't get money from Link machines, only NatWest branches are working.
A spokesperson said the bank is investigating the issue.
Sir Philip Hampton, who has been chairman of Royal Bank of Scotland since 2009, is to leave the bank next year for the same role at GlaxoSmithKline.
Royal Bank of Scotland, which has been based in Scotland since 1727, has said there are a number of "material uncertainties" arising from the Scottish referendum vote that could force its relocation to England.
A statement said the "uncertainties" could have a bearing on the Bank's credit ratings, and the fiscal, monetary, legal and regulatory landscape, adding:
For this reason, RBS has undertaken contingency planning for the possible business implications of a Yes vote.
RBS believes that this is the responsible and prudent thing to do and something that its customers, staff and shareholders would expect it to do.
RBS said any move to re-domicile the Bank's holding company and its main operating entity should have no impact on everyday banking services, while it would retain a significant level of its operations and employment in Scotland.
Standard Life has also advised investors it is "planning for new regulated companies in England to which we could transfer parts of our business if there was a need to do so".
Royal Bank of Scotland has confirmed it plans to move its holding company to England if Scotland votes for independence in next week's referendum.
The Treasury said last night that officials from RBS had told them the bank was ready to follow Lloyds Banking Group with plans to relocate to London in the event of a majority Yes vote next Thursday.
Shares in Scotland-based financial institutions Royal Bank of Scotland, Lloyds Banking Group and Standard Life fell by more than 2% in the wake of the latest opinion poll.
Perth-based energy supplier SSE was also fell.
Edinburgh-based Standard Life, which has been based in Scotland for 189 years, recently complained that it was still in the dark over "material issues" surrounding independence.
The Financial Services Authority, the FCA's predecessor, raised concerns in November 2011 about branch and telephone sales at RBS and NatWest but it was almost a year later before the firms started to take steps to put things right.
The firms made assurances to the FSA in July 2012 that the necessary changes were underway to address the regulator's concerns, but the FCA said this "failed to happen".
Where we raise concerns with firms we expect them to take effective action to resolve them without delay. This simply failed to happen in this case.
Taking out a mortgage is one of the most important financial decisions we can make. Poor advice could cost someone their home so it's vital that the advice process is fit for purpose. Both firms failed to ensure that their customers were getting the best advice for them.
The Royal Bank of Scotland will contact 30,000 mortgage customers who may be concerned about advice they were given by the state-backed bank after the Financial Conduct Authority found "serious failings" in its mortgage advice to consumers.
The City regulator said that only two of 164 sales made by the state-backed bank between June 2011 and March 2013 were considered to meet the standard required overall in a sales process.
It found RBS and its retail arm NatWest failed to consider the full extent of a customer's budget when making a recommendation, while staff did not advise customers what mortgage term was appropriate for them.
The regulator said there was no evidence that there was widespread detriment to customers, although RBS and NatWest will contact 30,000 consumers so they can raise any concerns they have about the advice they received.
RBS said that in response to the regulator's findings at the end of 2012, it overhauled its mortgage sales process and re-trained all mortgage advisers.
Royal Bank of Scotland has been fined £14.5 million by the City regulator for failing to ensure that advice given to mortgage customers was suitable.