China's biggest brokerage, Citic Securities, had overstated its derivative business by $166bn from April to September, according to the country's securities association.
Citic said the error occurred due to a system upgrade and has been corrected.
Probes have resulted in executives confessing to insider trading at Citic.
In September, shares of China's largest state-owned brokerage slumped after it reported that three executives, including its president, were under police investigation.
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