Category "nullreferenceexception"

What is a NullReferenceException, and how do I fix it?

I have some code and when it executes, it throws a NullReferenceException, saying: Object reference not set to an instance of an object.

HttpContext.User NullReferenceException only on deployed server

I am using formsauthentication on my MVC project and when testing locally using the Visual Studio Development Server everything works as expected. Once deployed