BuddyPress.org

The fatal error you are receiving is probably from not disabling buddypress linked plugins and THEN the actual Buddypress plugin itself BEFORE upgrading (Read more here – https://codex.buddypress.org/getting-started/upgrading-from-10x). I have crashed my site in the past from doing this. My theme itself really only has minor code changes and it’s not really possible to crash a whole site as it takes most of the code from the default theme.

The Unplugged theme also works ONLY with Buddypress 1.2rc+ and WordPress 2.91+. Installing Buddypress on a wordpress website in general may be a steep learning curve at the start but please read all the instructions on that link to guide you through.