Database diagram support objects cannot be installed (SQL Server 2005/2008)

Solution for the following error in SQL Server 2005 or 2008

Database diagram support objects cannot be installed because this database does not have a valid owner. To continue, first use the Files page of the Database Properties dialog box or the ALTER AUTHORIZATION statement to set the database owner to a valid login, then add the database diagram support objects." 

EXEC sp_dbcmptlevel 'SQLDBNAME', '90';
go
ALTER AUTHORIZATION ON DATABASE::SQLDBNAME TO "yourLogin"
go
use [SQLDBNAME]
go
EXECUTE AS USER = N'dbo' REVERT
go