On a project I’m working on, I had to set the database owner. So I opened up SQL Server Management Studio, opened the Properties for the database and tried to set the owner. But it failed with the following error:
The proposed new database owner is already a user or aliased in the database.
It looks like you cannot set the owner of the database to a user that is already used for this database. To fix it, you first have to remove the user from the list of logins.