Create a new database and user (it can be on the same MSSQL box/instance as the ppm/niku schema and database).
Did you restore from the dwh_mssql_base.db backup in your $NIKU_HOME/database/backups folder to get started with the seed schema information in your ppm_dwh database?
Have you used an MSSQL instance name, or a port number, in the settings? If both were populated, use one or the other.