Sadly I am having the same problem with a site I am trying to add this to. The site was configured for ASP.Net VB and the files have an .aspx extension.
I have IIS installed on my local machine and the testing server configured for it and when you press the test button, it says it connects.
The testing server setup:
Server Model: ASP.Net VB
Testing Server: H:\Inetpub\wwwroot\
URL prefix: localhost/
The webhost is also running a windows server, which is why I am running IIS on the local development machine.