A Nationwide spokesman said its online banking system was working normally after "a technical issue for a short while".
It earlier apologised for website problems.
Britain's biggest building society was forced to apologise to its customers again today after they were locked out of their accounts online for the second time this week.
The building society's mobile banking service was also unavailable tonight, but ATMs were operating as normal.
On Tuesday Nationwide apologised after an IT hitch stopped customers from accessing their accounts online.
Last July, the building society was hit by another banking error when nearly three-quarters of a million customers saw debit card payments taken from their accounts twice.
Nationwide corrected those mistakes and promised to reimburse anyone who incurred extra charges as a direct result.
Customers have vented their anger at NatWest & Nationwide after a computer glitch saw accounts mistakenly debited twice. Daybreak's Michelle Morrison reports.
A spokesperson for NatWest has said that they have solved their earlier computer glitches:
This is the second time in as many months that NatWest customers have suffered from banking problems. In June the bank suffered major technical problems and millions were left unable to withdraw money, check their balances or make payments.