This error is not easy to identify straight off. You will likely see an error screen similar to the one below, with the information in the 'Source error code' matching your error screen. You will experience this error on initially browsing to the web interface (not after logging in, etc). It is purely an IIS configuration issue.
You will note in the 'Parser error message' that this is caused by a virtual directory not being configured as an application. To understand how to solve this problem, please see the page on web application and pools.
See also