A recent monthly update to its Web site caused no end of trouble for online transaction company PayPal. But after an outage that plagued the site, PayPal appears to be back online.

According to a notice by eBay , which owns the PayPal service, the introduction of back-end code Friday morning to upgrade the site's architecture caused the Web site to crash, though not initially.

"The code worked well when tested and during the first hours of launch," a notice on the site said. "Unfortunately, problems handling peak levels of traffic developed later in the day that created intermittent availability and errors for members."

As of press time, access to the PayPal site appeared to be restored. "We have made good progress in our efforts to restore the PayPal site functionality," a note on the PayPal site said Tuesday.

"The PayPal site performed well during peak traffic levels this evening, and the overall member experience has improved significantly. Most members are now able to log in to the PayPal site to access account information, use shipping functions, use PayPal debit cards, and pay for items online with no difficulty. Should you encounter any errors when attempting to log in or use different PayPal functions, please try again."

Officials said they have no way of knowing how many transactions were lost since the code change. While some customers have been able to get online and conduct business, others haven't been so lucky. Tuesday afternoon, access to the Web site was intermittent. Sara Bettencourt, a PayPal spokesperson, said it was unclear how much had been lost in the meantime.

"We don't know that right now, because some of our users have been able to get into the site. They just experience slower-than-normal activities, so we don't know how many of our users have been affected," Bettencourt said.

She added that while parent company eBay normally pulls down buggy code and rolls it back to the previous version when it causes the site to lag, the architecture at PayPal doesn't easily accommodate a rollback. So developers from both PayPal and eBay have been working around the clock, Bettencourt said, to find the error in the site code and make the fix.

The crash is a setback for a company trying to keep its customers happy in the wake of a $9.25 million class-action lawsuit settlement in July, where the company allegedly restricted, froze or closed customer accounts. A Web site was set up to pay affected users $50 for their trouble; incidentally, that Web site frequently crashed or experienced slowdowns, though the actual site was hosted by a different company.

On Sept. 30, PayPal doubled its buyer protection plan from $500 to $1,000. The program, which begins in November, reimburses PayPal users buying goods on eBay that aren't delivered by a qualified seller.

The company has also taken other steps to appease its customer base. Last month, the company announced plans to levy $500 fines and possible legal action against Web site owners of porn content or services, prescription drugs and gambling who use PayPal to collect money. Ten days later, the company included PayPal users who used their account to pay for such services.

eBay officials are providing periodic site updates here.