Even as the Obama administration struggles to deal with the approaching end of open enrollment for health care exchanges, one critical part of the website has yet to be fixed.

Earlier, administration officials had predicted ObamaCare could be seriously jeopardized if the key back end of healthcare.gov were not fixed ahead of the March 31 enrollment deadline.

The back end of the website is the two-way connection between the government and insurance companies aimed at telling each other who signed up for what.

"Insurance executives just see this as a major nightmare," says Robert Laszewski of Health Policy and Strategy Associates. "I mean, when are we finally going to be able to reconcile all the data, to know who is really covered, who is really paid, and what the insurance companies should be paid for?"

Rep. Lloyd Doggett, D-Texas, raised concerns over it at a recent hearing with Kathleen Sebelius, the Secretary of Health and Human Services.

“The number that's really important," Doggett said, "is not how many people have enrolled, but how many people have paid their premiums that are actually getting in exchange-base coverage. A number," he said pointedly, "we've never been given."

Former Congressional Budget Office Director Doug Holtz-Eakin says,"Nobody knows.There remains no clear information about who has paid the premium and as a result, who the insurance companies need to get reimbursed for."

Though some analysts believe the administration knows a lot more than it is saying, officials deny having any reliable information.

Industry sources and surveys show that while officials boast 5 million sign ups, about 1 million of them are not paying premiums, and therefore not officially enrolled.

The administration hired the firm Accenture in a no-bid contract to fix the site after a previous contractor failed, arguing in official documents last December that there was no time for competing bids,since mid-March was a key turning point in the law, and any delay would, as the document put it, "... result in financial harm to the Government..."

It even went so far as to say that "... the entire health care reform program is jeopardized” by any failure of the back end, and it laid out a list of things that could go wrong, including "Inaccurate issuance of payments to health plans which could seriously put them at financial risk; potentially leading to their default and disrupting continued services and coverage to consumers..."

"This had to get fixed right now," says Laszewski. "Well it's past 'right now', it's - you know we're into March and we don't have the back end of the system done, we don't have the ability for insurance companies to be paid, we don't have the ability for reconciliations to be done."

Those reconciliations include who has really signed up, who has paid, and if the subsidies are accurate -- something officials say they don't currently know.

Sebelius tolda congressional committee recently,"people are buying a product in the private market. As soon as we have accurate information, we will give it to you but we do not currently have information about how many people have paid."

Officials now tell Fox News, however, that the dramatic language predicting possible disaster is "no longer an accurate assessment"because they're using temporary workarounds with insurance companies.

But the companies themselves say a reckoning is coming ... that could cost them tens of millions of dollars when the books are finally reconciled. And that could take months, well after insurance companies have to set new rates for 2015.