For fixing this:
You need to make sure that the directory from where you website is running is configured as an application in IIS. To do this, you need to go into IIS and find your project folder on the server, right click to Properties. Under Application Settings click Create.
and Change authentication mode to 'None' in web.config(if your application is running at a webserver not on local computer).
like this:
< authentication mode="None" />
hope it helps :)