It looks like you are trying to use this plugin – https://buddypress.org/community/groups/buddypress-activity-tags/ – because `Bp_Activity_Tags_Widget` is not in BuddyPress itself.
Try deactivating the plugin or, if you’re unable to log in to the admin, remove `bp-activity-tags` folder from the `wp-content/plugins` directory.
And maybe remove the short-code or widget corresponding to this plugin from your theme as well.
David, thanks for your help. I don´t have access to my site anymore (including the admin dashboard). I’ll try then to delete bp-activity-tags folder and then let´s see what happens.
David, you R a F genius! (= THANKS!) My site is working again! Now let me go to the forum question because I stil can´t get one single forum created.
Mr. David, you saved my site. thanks a lot dear. http://www.networkfriends.net