question about login at server level in sql server express

[Jean]

Hi,

I have a question about logins and sql server express and an ASP.NET
aplication. I put this question in sql server newsgroup, but without real
answer sofar.

I created a login 'Network service' at server level in Management Studio
express.
I use windows authentification.
Then i defined an user for my database which is associated to login 'Network
service', because the application asp.net uses that account (IIS 6.0). This
user received db_read and db_write roles.

This works.

Now i experimented a little bit and i removed from the logins at server
level the login 'Network service'.
Result: the application still works.
..
Then i removed the Builtin\users login from the login list at server level.
Result: i get the error: "login failed for Network service".

I recreated then the login 'Network Service' at server level but not the
Builtin\users login.
Result: it works again.

My conclusion is: one of the two logins must be in the list: Network Service
or Builtin\users

Is this right?
Why do i get that error when both logins are removed and not only when
Network Service is removed?

Thanks
Jean