I tried to run my WebApp on my local machine today (nothing has changed on it) and I had the above error. I know my machine had a windows update recently (not sure if that has anything to do with it).
The error produces a big print out of css styles and html markup.
In the markup it also says “The requested page cannot be accecssed because the related configuration data for the page is invalid”.
Maybe you accidentally changed the web.config and now contains a malformed section. I’d recommend you take a close look to your configuration file.
I’d say that the error page should tell you the necessary information to solve the problem but I assume that if you’re asking if because it’s not the case 🙂