DNN version 6.0
Running on PowerDNN shared server.
The mail test succeeds.
The syntax for my website entry in the MC settings is http://www.domain.com
When I test the MC settings the Green check mark is returned, but it states "Invalid Web Site".


Please advise.

Here are a couple things to try:

Make sure that the URL you have entered matches exactly what is in the browser address bar.
You may want to try adding the trailing slash.
Check your portal aliases, and make sure what you are entering exists, and is all lowercase letters.
Make sure you do not have a space before or after the URL.