PC manufacturers that expected to get their hands on the final version of Windows Vista yesterday will have to wait a couple more weeks for the OS, according to sources familiar with the Microsoft's plans.

The software giant originally targeted yesterday for Vista's RTM (release to manufacturing), but a last-minute bug that "took most of the Vista team by surprise" caused an unexpected delay, said Ethan Allen, a quality assurance lead at a Seattle high-tech company that tests its products for Vista.

Allen said the Vista team discovered the bug, which "would totally crash the system, requiring a complete reinstall", in Vista Build 5824 on 13 October. The team fixed the bug a week later in Vista Build 5840, he said, but it delayed the delivery of the OS to PC makers.

The team is now targeting a new date of 8 November, for Vista's release to manufacturing, Allen said. He also said that the business release of Vista, which Microsoft recently said is on track for release next month, "will barely make the end of November deadline".

Microsoft's US public relations firm disputed the claim that the business release would be delayed, and insisted the OS is still expected to be generally available in January 2007.

Vista's RTM isn't the only thing for which Microsoft is keeping people waiting. Consumers concerned about the change in Windows client licensing that will allow them to transfer a Vista licence only once are still wondering what happens when they switch the motherboard and other components of computers. Some power users, who like to build their own computers from scratch and rebuild PCs frequently, have wondered whether they will have to purchase a Vista licence every time they do this.

Microsoft is in no hurry to give them an answer. A week after users first raised the issue, Microsoft declined to comment, according to a representative from its public relations firm.