I installed MSE on several machines months ago, and these are legit systems with legit keys. However, as of today MSE is complaining.
Windows did not pass genuine validation. Security Essentials will become disabled in 28 days if you do not resove this issue. To continue using Security Essential, click Go online and resolve now and get genuine Windows.
What would have caused this to happen?
EDIT: These systems have been running years and never had any problems. So I know the keys are legit.