Upgrade Database from SQL Server 2008 to SQL Server 2008 R2
In this case, the error message is quite clear. You have backed up a database from a SQL Server 2008R2 instance and tried to restore it on a SQL Server 2008 instance.

It is not possible to restore databases to a previous version of SQL Server. This has to do with internal database structure differences between the versions. The only way to get your data from a SQL Server 2008R2 instance onto a SQL Server 2008 instance would be to export the data and import it. You could achieve this through SSIS, bcp, Replication or Linked Servers.