Hi,

Ah it seems like deleting user didn't delete friends. Will fix this in the next version.

In the mean time, if you would like to clean your friend list, please execute the this SQL (replacing 'prefix' with your database prefix).

delete from prefix_social_friends
where actor_id not in (select id from prefix_users)
or target_id not in (select id from prefix_users);

If you are not comfortable in performing this action, then please provide us your site's access and I will perform the clean up for you.