I upgraded the Simple Forum plugin. I got all kinds of error messages so after several tries the only thing that worked was to deactivate, uninstall (also drop SF tables). The end result was I lost all my "PAGES" and the linking ability of "TAGS". I can see my tags in the posts and tag cloud (I am on sidebar widget, simple tagging, simple tagging widget) but the tag links gives me a 404 message. This occurs on posts both prior and after the table drop.
The SF developer has been very helpful but says this is a WP issue now.
The tag problem occurred one week ago yesterday. As of yesterday my usual tag links on Google have gone away and what was steady traffic has slowed down 1000% it seems. It seems the bots can't see my tags, or maybe they see them but it goes nowhere (I guess I don't understand exactly how these bots work after this experience)
Revert to backup is not an option.