I have got following error message while restoring a backup from SQL Server 2000 to the latest version. I do not know the old version, now I am using SQL Server 2012 (11.0.3
You are trying to restore a SQL Server 2000 database on SQL Server 2012. This is not supported.
You will need to restore your database on an instance of SQL Server 2005, 2008 or 2008 R2 first, then back it up from there, then restore the new backup on SQL Server 2012. Microsoft explains this here.