eckhard If a fresh install of Hogfather doesn't work on your server there may be an issue with your server config. Could you tell more about your OS and phpinfo? I don't think Hogfather itself is broken - I'm even using it on my live site at stararmy.com/wiki right now and it runs fine (I did have to manually fix the XML sitemap though, which should be fixed in the next RC).
wolfgang-henderkes IIRC doesn't the bootstrap template include some plugin-like features and/or embedded plugins? You may want to make sure the bootstrap template is completely removed (rename its folder or something) and set the template to the normal Dokuwiki template and see if that works. Failing that, you could install a fresh Dokuwiki instance and simply move your pages and users into it from the original one.