hello, I am trying to add a user to a database but I get the error : Error 15023: User or role 'abacus' already exists in the current database. also, f I try to delete the user from sysusers table I get an error regarding cannot run ad hoc queries on system tables.
Why are you trying to add a user that already exists? Has the database been restored from another server and the user ids are messed up? If so, try the sp_change_users_login stored proc with the 'auto_fix' parameter to sort out the login.
If that doesn't work you can update the system table, but it's not recommended. Use the sp_configure option to set the 'allow updates' option to 1.