The COMException is caused by a few projects in my solution being bound to IIS rather than to the built in Web Development Server. I Asked on the ASP.Net Forums and you can follow the conversation here.
Studio apparently needs some rights (that it doesn't get by default) to read some info from IIS.
The work around is to launch Studio with "Run as Administrator" permission and all should work as expected.
I still consider it a bug that studio doesn't explain itself properly, but this workaround will do for now.