ASP.NET not detecting the current logged in user

what does it mean when my VB.NET returns:

Response.Write(System.Environment.UserDomainName)
returns "NT AUTHORITY"

and

Reponse.Write(System.Environment.UserName)
returns "NETWORK SERVICE"


instead of what it should be doing, which is:

Response.Write(System.Environment.UserDomainName)
returns "MY DOMAIN"

and

Reponse.Write(System.Environment.UserName)
returns "MY USER NAME"

My Go to the complete details ...