A database exists with no owner, likely caused by the owners user account being deleted.
You can use the following TSQL to set a database owner to sa. This replaces the deprecated function sp_changedbowner.
use [databasename]; GO ALTER AUTHORIZATION ON DATABASE::databasename to sa;
If you need help configuring alerts or anything else with your SQL Server, you can contact me (Steve Stedman) through my SQL Server consulting business Stedman Solutions, LLC.