Aetna Thursday withdrew plans to raise premiums on 65,000 customers who buy health insurance on their own, becoming the second insurer to do so in as many months because of "substantial mathematical errors" in its rate calculations.

The errors were discovered by state actuaries and by Aetna itself, which reported the errors to state regulators, the Department of Insurance said.

The company had been expected to raise rates on its California individual policy customers by an average of 19 percent.

"First, we found major problems with the Anthem Blue Cross rate filing," Insurance Commissioner Steve Poizner said today. "Now, additional scrutiny has revealed that Aetna's filing has significant mathematical errors."

Poizner recently announced plans to review rate filings by the state's four largest providers of health coverage for people who don't get insurance through work, including Aetna, Blue Shield, Health Net and Anthem Blue Cross.

As a result of the latest errors, Poizner said he would "take the exceptional step to post future individual health insurance filings on the Department of Insurance's web site."

Earlier this year, Poizner's department reviewed Anthem Blue Cross, which had disclosed its plan to raise rates by as much as 39 percent for 700,000 customers.

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