Error:
The specified SPContentDatabase Name=WSS_Content Parent=SPDatabaseServiceInstance Name=MSSQL2008 has been upgraded to a newer version of SharePoint. Please upgrade this SharePoint application server before attempting to access this object.
Reason:
This error may occur, if you are trying to attach the SQL server 2008 "MDF" file in SQL Server 2008 (No typo :) ) and the SharePoint Version is MOSS 2007 with no service packs.
Solution:
Just install the WSS service pack 2 & MOSS service pack 2. Now, you can attach the database without any issue.
For more info, refer my another post here
Thats it...