When reinstalling Dynamics NAV 2009 or if you have attached a Demo Database manually you will probably run into this problem:
Microsoft Dynamics NAV 2009 Build 27808
SQL Server option
Cronus Sample Database for Microsoft Dynamics NAV 2009
Fatal error during installation.
Error -2147467259: failed to execute SQL string, error detail: A database with name Demo Database NAV (6-0) already exists., SQL key: StopIfDatabaseExist SQL string: IF EXISTS (SELECT * FROM [master].[sys].[databases] WHERE name = ‘Demo Database NAV (6-0)’) RAISERROR (N’A database with name %s already exists.’,20,1,’Demo Database NAV (6-0)’) WITH LOG
The problem is here that a database already exists with from a previous installation. The problem can be solved by starting SQL Server Management Studio and deleting the database that already exists. After you have deleted the database start the installation program again and select repair. In Microsoft Dynamics NAV 2009 SP1 you will have one new option saying replace database that you can set to override existing database. If you need to save the existing database for some reason simple do a backup of it before deleting it or read my previous post about how to have more than one Demo Database installed at the same time.