England and Wales Cricket Board (ECB) let off Nottinghamshire with a fine of 600 pounds after Australian star David Hussey played in a Twenty20 match before he was registered.
Hussey smashed 60 as Notts beat Derbyshire at Trent Bridge, June 3.
ECB accepted that the county's failure to register the Australian properly was just a mix-up.
"It is accepted that this was an 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."
"Nottinghamshire apologised for its error and have put in place measures to ensure that such an error is not repeated in the future," ECB said in a statement.
ECB's discipline commission ruled that although Nottinghamshire gained clearance from Cricket Australia (CA), an "administrative oversight" meant Hussey should not have been fielded in the match.
"David Hussey is entirely blameless," the ECB statement added.