Bob Shlora of Alpharetta, Ga., was supposed to be a belated Obamacare success story. After weeks of trying, the 61-year-old told ABC News he fully enrolled in a new health insurance plan through the federal marketplace over the weekend, and received a Humana policy ID number to prove it.

But two days later, his insurer has no record of the transaction, Shlora said, even though his account on the government website indicates that he has a plan.

"I feel like this: My application was taken … by a bureaucrat, it was put on a conveyor belt and it's still going around, and it's never going to leave the building," he said. "I've lost hope. If it happens, great."

Obama administration officials acknowledged today that some of the roughly 126,000 Americans who completed the torturous online enrollment process in October and November might not be officially signed up with their selected issuer, even if the website has told them they are.

Technical problems surrounding the transfer of an applicant's personal information from the federal marketplace to the selected insurance company have plagued the system since its launch, making it difficult for insurers to finalize some enrollments. The 834 forms that issuers receive from the system have been riddled with errors, including often duplicate or incomplete information.

While the front-end of the website has been vastly improved, the back-end glitches remain a serious concern, IT experts and industry officials say.

"Until the enrollment process is working from end-to-end, many consumers will not be able to enroll in coverage," said Karen Ignani, president and CEO of America's Health Insurance Plans. "In addition to fixing the technical problems with healthcare.gov, the significant 'backend' issues must also be resolved to ensure that coverage can begin on Jan. 1, 2014."

Meanwhile for consumers, it's all turning out to be a giant headache. Shlora, who currently pays $2,800 a month for health care, told ABC News the "false braggadocio" coming from the White House is making it worse.

"The White House announced that they have met their goal," he said of the much-touted improvements to the website. "They are taking applications but they aren't going anywhere. What kind of goal is that?"

For those who thought they enrolled in a plan through the federal exchange since October, the Obama administration now advises that individuals contact their insurance company to verify coverage and if none exists, to start all over again.

"Consumers should absolutely call their selected plan, confirm that they have paid their first month's premium and that coverage would be available to them, beginning January 1 st," said Julie Bataille, communications director for the Centers for Medicare and Medicaid Services, or CMS.

"We will also make a concerted effort to reach consumers who selected a plan over the course of these past several weeks, so that they know what their next steps would be, which include paying their first premium and confirming enrollment with their plan," she said.

Federal health insurance helpers told Shlora to wait several days for a specialist from the website to get back to him, he said, while Humana has told him that his application may pop up by the end of the week.

In recent weeks, Bataille has repeatedly refused to discuss the scope of the back-end problem, declining requests for information about the error rate among the 834 forms and how many people might be affected.

CMS officials said today that a single "bug" in the system that prevented a Social Security number from being included in an application was the root cause of "more than 80 percent of the 834 production errors." Officials said that problem has been fixed, though they would not say when it was first identified and how many applications were flawed.