If you are using the Vail Public Preview that was released in August of 2010, please be aware that this build will be expiring on January 10th, 2011.
There is no workaround to prevent the build from expiring. If you have any data that you don’t wish to lose (which you shouldn’t as this is pre-production code), please back that data up before the 10th.
Microsoft announced in a forums post today that they are committed to providing an updated public preview build within the next 4-6 weeks.
Once a new build is released, you’ll find out about it here, the Microsoft forums, and the Windows Home Server team blog.