The software giant had won permission from the trial judge to do the test again after suffering two days of embarrassing gaffes over showing a flawed video of the test.

Microsoft spokesman Mark Murray initially told reporters Thursday morning: "I think that we've been able to resolve once and for all any questions about the videotape production."

But later in the day Microsoft had to admit things had gone awry again.

Microsoft said it could not get a consistent connection with the Internet to do the test. It was also supposed to do the test in the presence of government lawyers and computer experts but said it had barred Justice Department officials from entering the room while the computers were set up.

"Each time we connected we got a different performance rate, a different sized pipe," said Tod Nielsen, a Microsoft official. "So it would have been unfair to either side to compare, you know, one machine at one rate with another machine at another rate."

Microsoft general counsel Bill Neukom tried to dismiss reporters' questions about the credibility of Microsoft's tape as nothing but a "sideshow."

The Federal government and 19 states have accused Microsoft of integrating its Internet Explorer Web browser into Windows 98 so it could compete unfairly against a rival browser made by Netscape Communications Corp.

Microsoft first showed the video Monday to demonstrate that the browser was a part of the Windows operating system and that removing the browser in the way suggested by a government witness degraded performance.

But in two dramatic days in court, government lawyer David Boies challenged Tuesday whether the video was actually showing a computer with the browser removed in the way suggested by the government and Wednesday pointed out that the videotape seemed to have been spliced to show two computers as one.

The flawed video had shown the degraded rate. But Judge Thomas Penfield Jackson said that he believed the entire video had been discredited and he could not believe it.

At a bench sidebar with the judge Wednesday, Microsoft won permission to redo the video.

Government lawyer David Boies asked if government representatives could be present and a Microsoft lawyer agreed, as did the judge.

"Yes, that would be the best way to do it," said Jackson.

But when government officials arrived at Sullivan & Cromwell, the law firm representing Microsoft, they were barred from entering the room where the computers were being set up. They were later allowed in.

When reporters tried to question Microsoft's Neukom in detail about the reason the government lawyers were barred, he cut off the questioning with this comment:

"Call me old-fashioned, but I want to invite each of you to take just a minute today and think about my assertion that what you just witnessed this morning is thousands of times more material and substantive to this controversy and the PC software industry than this sideshow of melodrama about four minutes of tape."

He was referring to the testimony of Michael Devlin, who operates a software company. Devlin said that Microsoft provided helpful support to him in an alliance.

In answer to questions on cross-examination, Devlin acknowledged that he had told the Securities and Exchange Commission that any time Microsoft chose it could use information it gets from an alliance with his company to "develop or market competing products."