Transport for London (TfL) has said it is "aware of some problems" with its congestion charge payments technology, provided by IBM, according to Kable.
The system allows fleets, lease companies and vehicle rental suppliers to receive a £1 discount on the £8 congestion charge if they register their vehicles online so they are automatically charged when they enter central London at specified times.
IBM took over operation of the congestion charge in November 2009 from IT outsourcing firm Capita, after it built the online system.
It is believed that IBM slashed the system's administration costs by £75m when it took on the contract.
IBM's takeover of the congestion charge operation saw an upgrade of the computer systems that TfL said would save it £200m over the life of its current business plan.