Fix: Cannot use the special principal ‘sa’. Microsoft SQL Server, Error: 15405

When importing a database in your SQL instance you would find yourself with Cannot use the special principal 'sa'. Microsoft SQL Server, Error: 15405 popping out when setting the sa user as the DBO of the database. To fix this,

Open SQL Management Studio and Click New Query. Type:

USE mydatabase
 exec sp_changedbowner 'sa', 'true'