Hi Chi,
Are you trying to connect to SQL Server 2005 or 2000? If 2005, do you have the SQL native client installed? From what I have gathered from others who use Synchronizer, it is better to create a DSN to connect to the SQL Server, test it, then use the ODBC driver to use the DSN to connect to the SQL Server and synchronize. After that, change the driver in the Dictionary to MS-SQL.
Regards