When contacted, the LTA and the Network for Electronic Transfers (Nets), which issues the CashCards, would say only that they are working on a logistical solution. They gave no details.

It is still unclear where the problem lies - with the CashCards or the IUs - and motorists are getting frustrated.

Mr Francis Chua, 51, for example, said that he paid the fine the first time it happened, but has since made seven trips to the LTA office to get fine waivers.

He said that each of the seven times, the LTA sent him to a licensed vehicle inspection centre, such as Vicom, to get his CashCard and IU checked to confirm that it was a technical problem and not because his CashCard had insufficient funds.

Only then would the fine be waived.

'Each time, I waste 1-1/2 hours or more at the LTA office and Vicom to tell them about my problem and to get it verified - not to mention the 30 minutes' car ride in between.'

The chief executive officer of a semi-conductor company with 30 years' driving experience said his problems began in the last two months.

During this time, he has changed his CashCard six times - to no avail.

Among the 17 drivers interviewed, two said they had been fined seven times, one had been fined five times and the rest, once to thrice in the past year.

Drivers are hit with a fine whenever the ERP gantry does not detect the CashCard or the IU. Some drivers say they face the same problem entering carparks that use similar systems.

Contacted two weeks ago, Nets said the problem is due to compatibility issues with some IUs. It added that tests on its own IUs show that its CashCards are working fine.

But the LTA said the problem lies with a particular batch of CashCards issued in 2006 without the 'Gemplus' logo on the card's chip.

Another hapless motorist, Ms Stephanie Ong, tried to get the IU in her year-old car changed after being hit with fines five times and changing her CashCard four times.

Vicom, saying her IU was fine, refused to change it.

The marketing manager in her 30s said: 'In that case, I really don't know what the problem is. It leaves me wondering if it is going to be like this for the rest of my driving experience.'

A frustrated Mr Chua suggested that until Nets and LTA fixed the problem, fines should be automatically waived to save drivers the repeated hassle of seeking a waiver.

He also called for owed ERP charges to be payable through ATM machines, instead of only through Internet banking or at the LTA office.

tanwz@sph.com.sg