If you look close at the error, it will say
Module : IIS Web Core
This means it is coming from IIS. The problem is you do not have permission to access the config file. The error actually quotes config file as well, esp the line that says
<application path="/" applicationPool="mysite.hammadk.com"> <virtualDirectory path="..." > </appliation>
Go to the location where your config file is located. The IIS should give you that location in the error message. Right click in the folder and check directory permission. See what permission user ‘x’ has. In my case, somehow it has a cross sign on top of it. I dont know how it happened. It was working fine. Note that IIS is configured to access the site (and hence the location) via user ‘x’.