Apple has told iTunes users to "wait" before upgrading their computers to Microsoft Windows Vista, saying its music software may not work properly.
Popular music jukebox iTunes is not yet Vista compatible
The company said it is aware of several issues including problems playing purchased files and synchronising data.
Apple's support website said a new version of iTunes for Vista should be ready "in the next few weeks".
iTunes allows computers to synch data with iPods. Vista, the newest version of Windows was launched 30 January.
Apple outlined the compatibility issues and suggested workarounds for those already using Vista in a support document on its website.
Some problems listed were: failure to play music and video purchased from the iTunes store; poor animation performance; and a failure to automatically synchronize media, contacts and calendars.
Apple has also offered Vista users a downloadable tool that will "repair permissions for important files," but does not specify the precise nature of the incompatibility.
According to Associated Press newswires, the company has sold more than 90 million iPods since October 2001.
Microsoft has a team working with Apple to make iTunes fully functional on Windows Vista, Adam Anderson, a Microsoft Windows spokesman told AP.
He added that the company did not believe these issues were a reason stop using Vista.
When Vista launched, Microsoft said more than 5,000 hardware and software products were already compatible with the operating system.
Both Apple and Microsoft declined to comment on the issue further.