I recently restored a SQL Server 2000 database into SQL Server 2005. When I tried to create a database diagram I got the following error:
"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. "
After repeated attempts to to assign a valid login user to the database, I found this thread on the MSDN forums:
I issued the following command and viola! problem solved:
EXEC sp_dbcmptlevel 'EnterYourDatabaseNameHere', '90';
Just thought I'd share what I found...