2008 R2 Compatibility

It is not possible to restore a SQL Server 2008 R2 database on SQL Server 2008 due to the physical version numbers being incompatabile. You can run DBCC DBINFO to read the database header page to collect the actual information:

DBCC TRACEON (3604);
GO
DBCC DBINFO
GO
DBCC TRACEOFF (3604);

dbi_version = 661

A summary of versions

* SQL Server 7.0 databases have version number 515
* SQL Server 2000 databases have version number 539
* SQL Server 2005 databases have version number 611/612
* SQL Server 2008 databases have version number 655
* SQL Server 2008 R2 databases have version number 660

An excellant post The Rambling DBA: Jonathan Kehayias
and Paul Randal
explain this.