It took me some time to figure out that the most recent update produced several problems – either the blog is unreachable or some pages like “edit post” do not work anymore. In my setup this concerns the following plugins here

StatPress Reloaded
Lightbox Plus
WP-PostRatings ***
Yet Another Related Posts Plugin ***
*** make the site unavailable

So if you arrive here by a search engine: the only way to restart your blog (when you can’t even reach the plugins page) is to manually reset the entry of installed plugins to

UPDATE wp_options SET option_value = ” WHERE option_name = ‘active_plugins’;

or doing that manually using the phpAdmin interface. Finally, it was the old php memory problem as the php.ini was lost during the upgrade.