specialists said weeks of additional work lie ahead, including a major reconfiguration of the computer hardware, if the $630 million site, Healthcare.gov, is to accommodate the expected flood of people seeking to buy health insurance. Without the additional changes, experts predict, the website may continue to crash during periods of peak use. Beyond the prospect of potential delays for consumers, insurers warn that problems remain in the invisible “back end” that transmits enrollment information to them. That data has been plagued by inaccuracies, insurers say. Administration officials have been unwilling to disclose the error rate. As late as Wednesday, the site still continued to slow down when 30,000 users tried to log on simultaneously, according to project specialists. A batch of hardware upgrades and software fixes scheduled for this weekend, administration officials say, will allow the site to handle 50,000 simultaneous users, as promised, by Dec. 1, which is Sunday.