Redirect to Login Form automatically

Question

I working on Social Network.

It has a first Login Page. After Login I can navigate to many form in WebSite from Menus.

Here I have a problem with, whenever I trying to Click on Menu to open a web page, my website automatically goes on Login page.

It's happened sometime continuously, may be 2-3 time in day, or sometime work better.

Can anyone tell me actual problem of this website?