SendUsing Configuration is Invalid

[craigwfl]

This is really a lame error. I've spent two days scouring the internet
for a proper solution to my problem. My issue is that I have an ASP.NET
website using a VB.NET COM object to send emails (code below). This
sporadically works to send emails, but mostly gets the error mentioned.
Once an email does go out then the server sends emails fine until IIS
is reset.

I found this "SendUsing Configuration is Invalid" error attempting to
be addressed multiple times. The main solution is to make sure you are
assigning a server name to the SMTPMail.SMTPServer variable. This is
not the issue in my case. I have always assigned the Exchange server
via web.config and just recently added the three lines for oMsg.Fields
but that did not solve the problem either.

The only thing that addressed my issue for this is to install SMTP on
the web server. This makes no sense whatsoever! Emails would sometimes
go fine without the Fields lines and just an Exchange server. But once
SMTP is installed for IIS then it seems to allow all emails to go
through consistenly.

oMsg = New MailMessage
oMsg.From = MailFrom
oMsg.To = MailTo
oMsg.Subject = Subject
oMsg.BodyFormat = MailFormat.Html
oMsg.Body = Body
oMsg.Cc = strCC

oMsg.Fields("http://schemas.microsoft.com/cdo/configuration/smtpserverport")
= intMailServerPort

oMsg.Fields("http://schemas.microsoft.com/cdo/configuration/smtpserver")
= strMailServerName

oMsg.Fields("http://schemas.microsoft.com/cdo/configuration/sendusing")
= 2

SmtpMail.SmtpServer = strMailServerName
If (MailTo.Trim.Length > 0) Then SmtpMail.Send(oMsg)

For the moment, I think my situation is resolved in a less than
desirable fashion. I would love it if someone could tell me what I did
wrong or how to better resolve this issue.

Thanks.
Craig