Codeiginter 3 session problem

I have created a login page and when user logins and uses the system.
After some time the session expiry
Then login page comes to login
When user give information and login it is again coming to same page.

Kindly help me in this issue

I am having similar problems . I cant login at all , even when everything seems right ; no errors -- it just wont log in . I have been dealing with this for the past 3 days  and i thought i was the only one . Maybe i will just downgrade to 2, because my application worked 100% on it!