ACC is under the spotlight again after another client was sent someone else's private documents by mistake.
The Auditor-General's office and private auditors are already investigating how information about 6700 claimants was sent to Auckland woman Bronwyn Pullar last year.
The ACC chairman, chief executive and three board members have since resigned.
Now former Auckland builder Kahl Sharpe, 38, says included in his own ACC file, which he received on Thursday, was a five-page document about an Auckland brain injury victim.
"I would have thought they would have triple-checked it before it went out," he told the New Zealand Herald.
Mr Sharpe, who injured his neck and shoulder in 2008, is taking ACC to court to get it to pay for a recent shoulder operation that his private health insurance had to pay for.
ACC has paid for two previous operations and Mr Sharpe is on weekly compensation because of pain.
Outgoing ACC chief executive Ralph Stewart told the Herald the latest case was "human error".
"The mistake in the information was discovered and corrected in the client's electronic file, but overlooked in the large paper file that was released," he said.
"An internal investigation is under way into the circumstances of the breach and the errors that led to it."
The Office of the Privacy Commissioner has been notified.
KPMG auditors and Integrity Solutions, led by former Australian federal privacy commissioner Malcolm Crompton, are due to report to the Privacy Commissioner and the ACC board on August 23.
ACC Minister Judith Collins said earlier that she's "rebalancing" the corporation's responsibilities to restore public confidence, after the privacy breach and opposition attacks over the way it has "exited" thousands of long-term claimants over the last three years.
NZN