The "SendUsing" configuration value is invalid.
Typically this exception has to deal with the following line of code (or I should say ABSENCE of the following line of code):
SmtpMail.SmtpServer = "mail.your-domain.com"
Wanted to provide some additional information regarding a topic you have listed on SMTP and the SendUsing parameter.
Issue: Number=-2147220502(0x800403EA) App 
-2147220960[0x80040220]The "SendUsing" configuration value is invalid.
Additional Cause: The account running the code (usually a COM+ packaged component) which calls CDO (SMTP) does not have permissions to access the SendUsing configuration of the SMTP Metabase.
Additional Resolution: Run the adadd.vbs with the user account running the component code calling CDO.
Copyright © 2004 Contact: Dave Wanta.