I'm using SQL 2008 Express with a multi user VB.NET Windows application.

Do I have to add each user to the SQL user account? Does NT Authority\SYSTEM work? I do not know how this works. So far I have NT Authority\SYSTEM in the Security-Logins of the Server. But do I have to add it also in the database? In the databse Security-User, I have the following:

dbo
guest
INFORMATION_SCHEMA
sys

I tested the app in one of the users and it gives me error as follows:

Cannot open database "Print" requested by the login. The login failed.
Login failed for user domain\username.

What could be the reason?