If you tried to restore a SQL 2000 database backup into a SQL 2005. You will find out that the database diagram does not upgrade easily. If after restoring the database, you click on the database diagrams and get this 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.
There are 3 solutions to this problem:
a. if the default compatibility is other that SQL 2005(90), then set the compatibility level back to sql 2005. This is done by right click on the database then select properties --> Options.
b. Execute the following command on the query analyzer window
ALTER AUTHORIZATION ON DATABASE::your_dbname_here TO sathen after running this command, you can go ahead and add a new database diagram.
c. If you right-click the database you are interested on. Then select properties, select Files you will see that there is no owner specified on the text box for this database. Enter a valid userID (i.e. sa) in the box. Then the database diagram will start working.