PROBLEM WITH USERS ASP

I have one problem with the users in asp, I have 2 roles one administrator and one users and their respective users in each roles. but the problem its i cant acces for see my users and when I try to login in mi website I cant login because not detected the users but really exists, and later 5 minuts mi server detect mi users and the problem now its NT AUTORITHY NETWORK SERVICE and I already gave all folder permissions. I hope i can help me. my database its the default aspnetdb.mdf

...