Release-to-manufacturing pushed back to first quarter of next year.
Microsoft plans to release Windows Server 2008 by the first quarter of next year, breaking with the release schedule that projected a launch by the end of this year.
Release-to-manufacturing marks the stage at which hardware manufacturers receive the product, allowing them to start the qualification process and test it on their server hardware.
End users will not gain access to the technology until the official release. Microsoft attributed the latest delay to unspecified quality concerns.
"We would rather spend a little more time to meet the high quality bar that our customers and partners deserve and expect," Helene Love Snell, Windows Server product manager, wrote on a company blog.
The product is still scheduled for its official launch at an event in Los Angeles on 27 February.
Microsoft did not say whether the event will also mark the software's availability to end users. The current deadline could mark a launch as late as 31 March 2008.
The company pushed back Windows Server's availability for end users last month when it set the date for the Los Angeles launch event. Microsoft at the time denied that it had delayed the software, pointing to the release-to-manufacturing date.
The delay in the software's release is reminiscent of the trouble Microsoft had with the launch of Windows Vista.
The server and desktop operating systems were both developed under the 'Longhorn' codename, although they are distinctly different products.