How to fix orphaned SQL Server users

Make sure to run all listed commands from the database you are fixing, not from Master.

List the orphaned users in the database

EXEC sp_change_users_login 'Report'

To assign/repair with an existing login:

EXEC sp_change_users_login 'Auto_Fix', 'user'

To create a new login and password for this user, use this instead:

EXEC sp_change_users_login 'Auto_Fix', 'user', 'login', 'password'