When you run the InstallCertificate.exe from the Certificate package of a Windows Small Business Server 2011 Standard, on a Windows 7 or Vista Client, the Windows SBS self-issued certificate may fail to install.
The wizard was not run as Administrator. If it has been initiated from a Standard User Account, the Administrator password was not provided.
Run the Install Certificate Wizard as Administrator. Altenatively, run it using a Standard User and provide the Administrator credentials when prompted.