Some Wellington commuters who use a prepay card were overcharged on Tuesday due to a technical glitch.
The plastic Snapper bus pass was introduced in July last year.
NZ Bus general manager Zane Fulljames says the problem occurred when new software was installed wrongly on 12 of 40 Go Wellington buses.
Weeks ago, drivers told Radio New Zealand that they were fed up with the system's software problems.
Mr Fulljames says Go Wellington and Snapper are tracking down 101 people who were overcharged to give them a refund.