BuddyPress.org

This is line 566:
if ( !$domain = wp_cache_get( 'bp_user_domain_' . $user_id, 'bp' ) ) {

It sounds like you’re using some type of caching on your site. Try turning it off to see if the error goes away.

The function where this line resides — bp_core_get_user_domain() — only outputs a link to the user’s profile. Without knowing too much about your code, there’s not much we can do on our end.