I hope that you have migrated database from Express to SQL2008 Standard.Now you have to use this database as a custom database for Single sign On so you have to create tablespaces manually for single sign on.I believe that you want to upgrade VC from 5.0 to 5.1 but there is no single sign on in 5.0 so first you have to create DB,table space and users for single sign on. provide proper privileges to both users then proceed single sign on installation.
Thanks,
Atul
