Deborah Whitman, director of Microsoft's new small-business portal, bCentral, said an employee shortage was to blame for an increasing lag in turnarounds from about 24 hours to as long as 10 days.
"We have to look at every banner so that one doesn't get into the network that would make people upset," she said. "We are backlogged on that right now."
Whitman said the company brought in new staff three days ago to help out with the backup.
One LinkExchange customer said he could not get a new ad posted for three weeks, despite a flurry of email complaints. In one reply, LinkExchange refused to provide telephone support, saying it could offer better service by email.
"Regarding your phone request, we have found that the type of information we deal with can be relayed much more efficiently through email," the reply said.
Whitman defended the policy, saying that most customers found email support adequate. She said LinkExchange does answer telephone inquiries, although no telephone number is listed on its Web site.
The banner ad delays come at an awkward time for Microsoft, which has been seeking to bolster its MSN online service with new offerings such as bCentral, which launched in mid-October. The site aggregates MSN's small-business services, which include LinkExchange, travel Web site Expedia and headlines from MSNBC.
bCentral competes with Netscape's Netcenter portal, whose successful focus on business users was said to have been one of the main reasons America Online acquired Netscape early this year. Other portal sites, including Yahoo and Lycos, recently have bolstered their small-business offerings as well.
The banner ad delays also come as competitor DoubleClick is aggressively moving to build on its lead in the online advertising market.
DoubleClick, which delivers ads for more than 1,500 Web sites, has gone on an acquisition spree, inking deals recently with Opt-In Email.com, Abacus Direct and NetGravity. On Monday, the four-year-old company released a suite of products marking its official entry into the email advertising arena.
bCentral's Whitman said LinkExchange has done well in the marketplace, growing from 600,000 active users since July 1998 to more than 1 million active users today.
LinkExchange offers several levels of service. Premium users who pay $19.99 a month receive 5,000 banner ad impressions, search engine submission services and an email marketing list, Whitman said. Despite recent delays in posting new ads, such customers will receive the full 5,000 impressions, she added.
News.com's Jim Hu contributed to this report.