Error restoring backup in sql server. Old server version
While you may have SQL Server 2008 R2 on your machine (or at least the management studio), that doesn't stop you having or connecting to a SQL 2008 Server - which it seems you are.

 select @@version


will tell you the server version and its number.

10.50.2500 is SQL 2008 R2 SP1

10.0.2573 is SQL 2008 SP1

NB - SQL 2008 SP2 (Service Pack 2) is different to SQL 2008 R2.

To restore this backup, you need to connect to a 2008 R2 or 2012 server.