A fault with Belfast's new bus lane cameras has led to more than 700 fines being scrapped - just a month after they were introduced.
An average of 25 penalty notices a day were issued in error in the first four weeks.
It involves up to £65,000 worth of fines.
The problem only came to light after concerns were raised by members of the public who received inaccurate penalty notices.
Regional Development Minister Danny Kennedy apologised for the "unacceptable" blunder.
However, it has led to concerns that the system is unreliable.
SDLP MLA John Dallat said: "Many members of the public will have no confidence in the ability of these firms to operate a system that is reliable and not reliant on the general public to report faults.
"More so, they will want to know why a Government department accepted this system without its accuracy being authenticated independently before starting to churn out fixed penalty notices at £90 a time."
Earlier this year legislation was passed allowing the Department for Regional Development to monitor and fine drivers using the city's bus lanes.
Motorists are hit with a £90 fine - reduced to £45 if paid within two weeks - each time they drive in a bus lane.
A total of 1,273 drivers were caught in the first week after the fine system started on June 22.
However, it has now emerged that 730 penalties issued between June 22 and July 21 contained errors.
A total of 118 were wrongly issued.
In another 612 cases, incorrect camera settings meant the time stamp on penalty notices was inaccurate, and these have also been cancelled.
NSL, the operators of the bus lane cameras, said it has identified what went wrong and has taken steps to ensure there is no repeat.
However, David McNarry, who sits on the DRD's scrutiny committee, said: "It is a disgrace - a complete farce.
"Not only is the department intent on persecuting motorists, it has made a complete cock-up in doing so."
NSL blamed a "process configuration error" for the fault.
Executive director Nigel Coltman said: "We know that this error with the timing settings on the enforcement cameras should not have happened, and because of the measures we have taken, we are now sure that it will never happen again."
Mr Kennedy said he was setting up an independent review into the blunder.
"Bus lane enforcement has been in place since June 1 with the aim of improving public transport. To find out that there has been a fault with the system is unacceptable," he said.
Bus lanes were introduced in Belfast in October 2012. A crackdown on drivers using the lanes began last month, with the introduction of six cameras in the city centre and a mobile detection unit.
The fixed cameras are located at:
• Great Victoria Street, near the Europa Hotel.
• College Square East, near Belfast Inst school.
• East Bridge Street, near Central Station.
• Castle Place, near Royal Avenue.
• And two at Belfast City Hall.