Instructions for Customers needing to re-add and re-link database users:
As for the procedure, you must open ssms (SQL Managment Studio) and add the missing user to these 2 areas:
Databases > [database_name] > Security > Users > [username]
General:
user name -> the user name
login name -> the login name (same as user name)
default schema -> dbo
Membership:
(check all options except db_denydatareader and db_denydatawriter)
Security > Logins > [username]
General:
login name -> the user name
SQL Server authentication
Password/Confirm Password -> enter the password
Enforce password policy (deselect)
Default database -> select the associated database
Once the user is added, re-link the user with the login via New Query, plugging in the proper database name and user names:
use database_name
go
EXEC sp_change_users_login 'Update_One', 'theusername', 'theusername'
go
On success, user should now be created and linked correctly to the database.