if you’re running Visual Studio (for me, it was 2010), and you start debugging your ASP.Net site, and you get the error in the subject line (with your specifics where the dots are), it can be a harrowing experience trying to find the solution.

What I did to correct the problem was to go inside the web applications project properties, and under ‘Servers’, uncheck ‘Apply Server settings to all users’. Also, uncheck the radio button entitled ‘User Visual Studio Development Server’. For me, before I did that, I also changed the port number.

Next, I clicked to choose ‘Use Local IIS Web Server’/IIS Express, which ended up with the Project URL as http://localhost:3900 (being the new port number I assigned). I believe I clicked the button to create the virtual directory, but at this point, I don’t know how necessary that really was.

Anyway, voila – my site was up, running and debuggable (that’s now a new word)!