I take it your using V3.4.02? I'm also getting this error and I've already asked the question earlier but no one has answered yet. So I'm still using V3.4.01. I still think there was a problem with the code release for .02 but I cannot seem to target were it was.
As your the second person to come along with this exact error I cannot fathom why no one else appears to have had the same problem or indeed come up with a possible solution.
I have it working now. I think it happened when I put an @sign in the mail server name or possibly because I didn't leave it blank when I was using CDONTS mail.
It would have been nice if the error was more specific.
Are you positive that's all you did? I've changed both of these so that it was either blank when using CDONTS or had an entry when using ASPEMail or JMail.
I still can't get it to work (even though I've now upgraded to V3.4.03!).
Any further advice you can offer Zenfor (or indeed anyone elses help is appreciated.)