More than 1,800 motorists are being told that fines and penalty points issued to them are being revoked.
It comes after An Garda Síochána and GoSafe identified that a static speed camera on the N17 near Claremorris in Co Mayo was not certified.
It was, however, fully functional and accurately identifying offences.
Some 1,871 speeding fixed-charge notices - issued between 20 December 2024 and 12 February 2025 - are being revoked.
Gardaí have begun writing to the motorists affected and said that refunds will be issued with penalty points removed where necessary.
Drivers impacted do not need to do anything and will receive a letter in the post.
However, if they have further concerns they can ring the Fixed Charge Notice help desk on 0818 50 60 80.
Certification error fixed on 13 February
Of the 1,871 fixed-charge notices issued - 800 were paid and penalty points applied, 123 were paid but the error was identified prior to penalty points being applied, and in the remaining cases, no payment was made before the error was identified and no penalty points were applied.
The camera issue was identified on 12 February. It was certified the following day and has been operational again since 14 February.
Gardaí said it is standard procedure that all cameras used for speeding detection have valid calibration certificates issued by GoSafe.
The more than 230 speeding fines issued from the system on the N17 since 14 February are valid, a statement added.
In addition, An Garda Síochána confirmed that all certificates of calibration for cameras used at average speed, static locations and in safety vans are valid.
The force said that both it and GoSafe have put measures in place to prevent a recurrence of what happened.
The issue arose as the original camera used during testing had a faulty focus mechanism and when a new camera was installed it did not have a valid certificate of calibration.
The N17 system went live on 20 December 2024. It was not operational between 1 January and 17 January 2025 as it had been vandalised which is the subject of a criminal investigation.
The 1,871 speeding fixed-charge notices were issued over a period of 39 operational days.
There were no summons issued relating to non-payment of these fines.
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Chief Superintendent of Roads Policing Jane Humphries said: "This error is very much regretted. An Garda Síochána is committed to reducing road deaths and serious injuries through enforcement of speeding via a variety of speed safety cameras.
"The level of speeding breaches issued since the camera went operational on December 20, 2024 demonstrates the continued need for all motorists using this road to slow down."
A GoSafe spokesperson said: "At GoSafe, we are committed to maintaining the highest standards of quality and safety.
"During a routine quality assurance check, we identified that the calibration certificate for radar components in a static speed camera on the N17 in Mayo had expired. The accuracy and validity of the camera system was not affected at any time and all speeding offences were correctly identified.
"However, it is standard procedure that all cameras used for speeding detection have valid calibration certificates. The radar component of the camera in question has since been recertified and cleared without issue.
"Following a thorough internal review, we have confirmed to An Garda Síochána that all other static, mobile, and average speed enforcement cameras are fully certified. To prevent a recurrence, we have implemented enhanced safeguards within our quality assurance processes.
"We remain steadfast in our dedication to supporting An Garda Síochána and all other road safety stakeholders with reliable, rigorously tested technology that ensures public trust in road safety measures."
The Road Safety Authority said the "situation is regrettable" but "it does not diminish the effectiveness of speed cameras in saving lives and reducing serious injuries on our roads".
In a statement, the RSA said that it "continues to support the use of enforcement technology as a critical tool in addressing speeding, which remains a leading cause of road deaths".
Minister for Transport Darragh O'Brien said he only learned of the error today and it is not entirely clear how the issue arose.
"I do take it very seriously and I will be looking into it. There will be lessons from this. We're going to have to double check that certification of all speed checks is exactly as it should be.
"Motorists who have been impacted will need to have their licences updated and it is a priority now to identify those as no one should be carrying penalty points that were detected in error, but I do need to examine this matter in more detail," Mr O'Brien said.
Additional reporting Cathy Halloran
