This error can occur if the database has been updated to a version of SQL Server that is higher than the version of SQL Server you are attempting to attach it to. Once a database has been attached to a specific version of SQL Server, it cannot be attached to a lower instance of SQL Server. For example, if you attach your database to a SQL Server 2008 R2 instance, it cannot be attached to a SQL Server 2005 or SQL Server 2008 instance, but can only be attached to a SQL Server 2008 R2 or higher instance.  The error can also occur if you select an incorrect SQL Server instance when attaching a database.

To resolve this error, attach the database to a version of SQL Server that is the same or higher version than what is was attached to previously.

If the SQL Server and database version is correct, and  the issue still persists, attempt the following:
  1. Ensure the SYSTEM account has Full control of directory where the database is located.
  2. When attaching the database, select the option to Select another SQL Server instance
  3. Manually specify the SQL Server instance instance in the Select Server field of the Attach Database Wizard.
  4. Use SQL Authentication for the Login Information method and continue through the Attach Database Wizard.