logged in members are required to sign in again to view social group

[JohorBahru]

I've changed "calender" on my navigation bar to "social group".

However, my logged in members are required to sign in again to view the social group page.

It always prompt my logged in members with the message as:

You are not logged in or you do not have permission to access this page. This could be due to one of several reasons:

1. You are not logged in. Fill in the form at the bottom of this page and try again.
2. You may not have sufficient privileges to access this page. Are you trying to edit someone else's post, access administrative features or some other privileged system?
3. If you are trying to post, the administrator may have disabled your account, or it may be awaiting activation.

May I know how to solve this issue?

thank you