Description
The Web application at http://localhost could not be found. Verify that you have typed the URL correctly. If the URL should be serving existing content, the system administrator may need to add a new request URL mapping to the intended application.
Reason
Maybe it configures not correct for the Target Framework or the Platform Target in the project Property.
Solution
Target Framework: make sure to select correct framework.
Platform Target: it is better to select “Any CPU”.