If you are using the Windows 8 Developer Preview it is due to expire on March 11th. Now Microsoft have released a fix to extend the date.
The update postpones the expiration date for Windows 8 Developer Preview and for Windows 8 Server Developer Preview. Currently, the expiration date for Windows 8 Developer Preview is set to March 11, 2012, and the expiration date for Windows 8 Server Developer Preview is set to April 8, 2012. After you install this update, both expiration dates are postponed to January 15, 2013.
That being said, the Consumer Preview will be released later this month so I would be really surprised if that many people would still be using the Developer Preview after that date.Download the fix from here