If you only detach and attach the database of SSO, you lose the users, cause they are defined in master database, not in SSO database.
To fix it, go to the new SQL Server, and using SQL Management Studio, create the logins of SSO database and map to SSO database.
Here are some help about detach/attach SQL Server database:
Understanding and dealing with orphaned users in a SQL Server database
http://www.serverintellect.com/support/sqlserver/sql-database-attach/