Bumbling car park attendants ticketed motorists at Aylesbury Shopping Park after forgetting to put the clocks forward on their machines.
The clocks on ticket machines at the retail park, which is home to outlets such as Argos, PC World, Wickes and Costa Coffee, were running an hour behind on Sunday.
It meant that drivers who expected two hours of free parking in fact only got one.
Tristan Floyd, from Stone, was one of many wrongly slapped with a £90 parking penalty.
Mr Floyd said: “I brought a ticket at 10.57am but the clock on their machine said 9.57am.
“I was most surprised when I was sitting drinking a coffee in Costa at 12.30pm and saw a parking attendant putting a ticket on my car.”
UK Parking Control acknowledged the error and said it was writing to affected motorists to apologise.
A spokesman said: “We can confirm that the hour amendment to the time on the pay and display machines was scheduled for early Sunday morning.
“However it was brought to our attention on Monday morning that there had been a delay causing some charges to be issued incorrectly.
“All charges issued for displaying an expired pay and display ticket prior to the time change have been cancelled in full and an apology letter has been sent out where possible.”