SQL Error 15023: User already exists in current database !

Solution :

USE YourDB

GO

EXEC sp_change_users_login 'Report'

GO

to check if there are any orphaned users.

then next map your user with its respective login. If the user does not exist try

USE YourDB

GO

EXEC sp_change_users_login 'Auto_Fix', 'user', NULL, 'password'

GO

this will work perfectly.......