BuddyPress.org

@beginner3 I’ve updated the screenshot in the link you posted. There’s only one “Save Settings” button on that page now. Sorry for your confusion.

>> keep getting the above error message
That happens when you enabled registration in your site but haven’t published blank Register or Activate pages in your site.

How do i Publish those pages?

Let me google that for you:
http://easywpguide.com/wordpress-manual/saving-and-publishing-content/

> I meant how do I disable registration?
Go back to where you enabled it in Settings > General for single site or in Network Admin > Settings if you’re on multisite.

I have published blank Register and Activate page on my site but I keep getting the error message?

@beginner3 If you have enabled registration again, then go wp-admin menu Settings > BuddyPress and click on the “Pages” tab, and in the Registration and Activate section, choose the blank pages you created and associate each with respective functions per

>> there is not Save Setting button to allow me to save the changes

@beginner3 You mentioned in your original post that you already “have tried to deactivate delete and reinstall plugin”, so at this point we need you to provide more information about your installation to help you troubleshoot https://buddypress.org/support/topic/when-asking-for-support-2/