Microsoft and other businesses headquartered in Washington State can't use Windows Vista-based PCs to pay their unemployment insurance taxes online because the operating system is incompatible with the state's electronic filing system, according to a bulletin published by the State of Washington Employment Security Department.

The bulletin, which appears on a state run Web site, notes that users of Washington's UIFastTax system "have reported having difficulty with oursoftware on the new Windows Vista operating system." The bulletin further notes that, "At this point, we are unable to support Vista."

That means Microsoft and other companies that have to pay taxes to fund unemployment insurance in Washington State will have to use computers running an older version of the Windows operating system if they want to file electronically.

As long as they don't use MSN, that is. The state-run Web site further notes that computer users who access the Web through Microsoft's Internet service could have trouble logging into the system if they also use PCs running the Windows 95, Windows 98, or Windows ME operating systems.

For such users, Washington's Employment Security Department offers a less- than-hi-tech fix: "It is recommended they use the File Offline feature in UIFastTax."

Compatibility issues are causing some potential Windows Vista buyers to think twice about upgrading to the operating system. Officials at the Federal Aviation Administration, for instance, have said they may pass on moving their 45,000 desktop and laptop computers from Windows XP to Vista in part because of such concerns.

Microsoft officials have insisted that some compatibility problems are to be expected with the rollout of any new operating system. Windows Vista officially launched on Jan. 30.