SQL 2005 Database Diagrams Error: "database does not have a valid owner"

Ok, I've been bitten by this twice now, so here is the error and solution:

Error:

TITLE: Microsoft SQL Server Management Studio
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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.

Solution:

In my case, it's because my domain login is set as the database owner but I am working remotely.  My PC can't validate my login against the domain, so SQL Server errors out with "invalid owner".

The easy solution is to change ownership of the database to sa, using sp_changedbowner.