ASP .Net tab missing or SharePoint site leading to Page not found and IIS 32/64-bit modes

Problems:

ASP .Net Tab Missing in the IIS Managers Website properties
SharePoint site shows “Page cannot be found error”.
SharePoint sites shows “You are not authorized to view this page”, “HTTP Error 403 – Forbidden: Access is denied.”
Either of the above problems in a server farm.

Possible Solutions:
There could be couple of reasons for the ASP .Net tab missing [...]

IIS Authentication Model and Options

IIS 6.0 Authentication Model: An important part of many distributed applications is the ability to identify someone, known as a principal or client, and to control the client’s access to resources. Authentication is the act of validating a client’s identity. Generally, clients must present some form of evidence, known [...]