When you try to attach a higher version database to lower version sql server(attaching sql2008R2 database to sql SQL2008 Instance),you will get an error message similar to “The database is of version 661. The server will only support databases of version 655 and earlier”. This is error simply means that you are trying to attach higher version database to a lower version sql server.This is not suppported by SQL Server.Remember, we also cannot restore higher version databases to lower version sql server.Below are reference internal numbers for each of version of SQL Server:
Internal Version Number = 611 == SQL2005
Internal Version Number= 655 ==SQL2008
Internal Version Number= 661 ==SQL2008R2
Internal Version Number= 706 == SQL 2012
If you want to find out the database Internal version, run the below
DBCC TRACEON(3604)
GO
DBCC DBINFO('DatabaseName')
GO
DBCC TRACEOFF(3604)
In the results, look for dbi_version.There is also dbi_createVersion and this shows the actual version it was created on.
Example: if the database was created on SQL 2005 and later migrated to sql 2008R2).
In that case, you would see, dbi_createVersion = Internal version number the database was intially created which is sql 2005 Internal Version Number as per example and dbi_version = shows the present Internal version number which is sql 2008R2 Internal Version Number
SQL Server Repository 