I always tend to forget the order of this. A short summary for restoring a Sql server .bak file:
1. Restore database. (Run Sql Server Manager as admin, make sure you window user have access rights to appropiate folders etc).
2. Delete the accompanied database user that is on the “database”. (user should be on database server scope not on the database)
3. If there isn’t already a user on the database server user level, create one, and set the user mapping for user -> database owner of -> newly restored db.