If SQL Server is not installed on your system, or the version does not match the version of
the file, Server Explorer may refuse to open the aforementioned database file, stating that
it isn’t compatible with the current SQL Server instance. In that case, the Microsoft knowledge
base article at http://msdn.microsoft.com/en-us/library/hh873188.aspx provides
instructions to upgrade the database file to either a more recent version of SQL Server
Express or to the new LocalDB format.