Fix: User, group, or role already exists in the current database. (Microsoft SQL Server, Error: 15023)

Run following T-SQL Query in Query Analyzer to associate login with the username. ‘Auto_Fix’ attribute will create the user in SQL Server instance if it does not exist. In following example ‘ColdFusion’ is UserName, ‘cf’ is Password. Auto-Fix links a user entry in the sysusers table in the current database to a login of the same name in sysxlogins.

USE YourDB
GO
EXEC sp_change_users_login 'Auto_Fix', 'ColdFusion', NULL, 'cf'
GO

Reference: http://blog.sqlauthority.com/2007/02/15/sql-server-fix-error-15023-user-already-exists-in-current-database/