Two and a half months after the troubled launch of HealthCare.gov, the Obama administration today disclosed the scope of problems on the website's back-end, revealing how many Americans might not have the health insurance they think they signed up for.

The Centers for Medicare and Medicaid said today that applications for as many as one in four people who selected a health plan on the site in October and November may be in limbo due to technical glitches with the so-called 834 forms that get sent to insurers to complete the process.

While officials claim many of the problems have since been resolved, the current application error rate stands at about one in 10, they said.

CMS and the White House have urged anyone who signed up through the federal online insurance portal to call their insurer to verify their enrollment, and if no record of the purchase exists, to start over with the sign-up process immediately. The administration says more than 155,000 Americans selected health plans through the federal exchange between Oct. 1 and Dec. 2.

Since early October, issuers and some consumers have complained about faulty enrollments because of problems in the data pipeline between the website and insurance companies. Today, CMS outlined three distinct categories of trouble that they are still scrambling to resolve.

"Issues involving 834 transactions fall into three categories: one, forms that may not be generated from the system; two, duplicate forms being generated; and three, forms that may have passed technical data incorrectly," said CMS spokeswoman Julie Bataille.

"Our dedicated 834 team, operating with the speed and urgency of a high-performing private sector tech company, now being overseen by our general contractor, QSSI, is working directly with issuers to systematically go through this information and resolve any remaining issues," Bataille said. "Our clear priority is fixing any remaining bugs that are causing problems and working to make sure that every 834 form, past and present, is accurate."

Bataille said CMS has instituted a "more rigorous monitoring system and feedback loop less reliant on anecdotal information" to track accuracy of 834 forms going forward.

As for the revamped consumer-facing, front end of the site, CMS says it was "working well for vast majority of users" this week, the first since major repairs were completed by Nov. 30.