The Obama administration acknowledged Thursday it has been over-reporting the number of people signed up under the health care law, a discrepancy that congressional Republicans seeking to repeal the program say they uncovered.

It’s another credibility problem for the administration after video surfaced recently of former White House adviser Jonathan Gruber suggesting that deception was used to pass President Barack Obama’s signature law.

Health and Human Services Secretary Sylvia M. Burwell called the latest lapse “unacceptable.”

“The mistake we made is unacceptable,” Burwell said on Twitter. “I will be communicating that clearly throughout the (department.)”

Administration spokesman Aaron Albright said that the overcount involved about 400,000 people.

Those consumers have separate dental coverage in addition to a medical plan, and were double-counted by mistake, said Albright. They had purchased both the medical and dental plans through HealthCare.gov and state insurance markets created under the law.

That means the correct number of people enrolled for medical coverage as of Oct. 15 is about 6.7 million, not the 7.1 million that Burwell has been citing.

The discrepancy was uncovered by Republican investigators for the House Oversight and Government Reform Committee, poring over sign-up spreadsheets.

Chairman Darrell Issa, R-Calif., said in a statement that he believes the administration was deliberately trying to disguise the rate at which people have been dropping out of the program, either because they don’t meet eligibility requirements or weren’t paying their premiums.

“Faced with large numbers of Americans running for an exit from Obamacare, instead of offering the public an accurate accounting, the administration engaged in an effort to obscure and downplay the number of dropouts,” said Issa.

Responded administration spokesman Albright: “No. It was a mistake.”

Back in May, the administration reported that more than 8 million people had signed up through the new insurance markets, which offer taxpayer-subsidized private plans. That was celebrated as vindication for the health care law after the botched rollout of HealthCare.gov.

The 8-million number was always expected to go down, because it included people who had not yet sealed the deal by paying their first month’s premium.

The next update came in September, when Medicare Administrator Marilyn Tavenner told Issa’s committee there were 7.3 million people enrolled at that point. Burwell has later revised that number down.

After Tavenner testified, Issa’s committee requested the underlying files, and a spokeswoman said investigators dug in, discovering the overcount.

In recent months the administration has drifted away from issuing formal status reports on the health insurance exchanges, instead releasing snippets of information, as Tavenner did before Congress. Compiling the formal reports is a time-consuming exercise, but it also involves repeated edits, which can catch errors.

Thursday’s development comes amid a still-simmering controversy over comments by MIT economist Gruber, an adviser during the drafting of the law. Video clips show him saying that “the stupidity of the American voter” helped Democrats pass the health care makeover.

Gruber has since disavowed the most controversial remarks, saying he “spoke inappropriately and I regret having made those comments.” But the videos have fired up opponents of the law, who are calling on the new Republican-led Congress to mount an all-out effort for its repeal.

The enrollment overcount was first reported by Bloomberg.

(AP)