Every several weeks I was haunted by this annoying problem and waste my life for hours!!! This time, I am gonna file it down for future and also others.

Symptom:

Site.css file under "Styles" folder cannot be accessed

And, page will be appeared like this:

Even after the following code have been added in the web.config file:

And even after the identity of application have been set to Administrator:

Solution:

Add Users account to the permission list

When will we encounter such a problem:

When we deploy the project file in User folder in c:/ drive or in a Mesh share folder

And

Result:

ASPNET