The ECB have fined Nottinghamshire for fielding Australia batsman David Hussey in a Friends Life t20 match without registering him.
The cricket discipline commission ruled that although the Outlaws had gained clearance from Cricket Australia, an "administrative oversight" was responsible for Hussey being unregistered for the clash against Derbyshire.
As a result the county have been fined £600, although Hussey, who went on to score 60 in the victory at Trent Bridge on June 3, was cleared of any wrongdoing.
An ECB statement read: "The ECB today announced that Nottinghamshire County Cricket Club has been fined £600 by the cricket discipline commission in respect of an offence of playing an unregistered player in a Friends Life t20 match earlier this month.
"After investigation, it is accepted by the commission that the failure to register was an administrative oversight on the part of the county and that the player - now registered for that county - was at all relevant times eligible to be registered to play for Nottinghamshire and that Nottinghamshire had obtained the necessary No Objection Certificate from Cricket Australia.
"The player himself, David Hussey, is entirely blameless.
"In these circumstances the matter has been dealt with by way of summary procedure.
"However, the commission wishes to underline the need for counties to ensure that players are properly registered and in timely fashion.
"Nottinghamshire County Cricket Club apologised for its error, accepted the financial penalty and have put in place measures to ensure that such an error is not repeated in the future."