Preview is broken

When I try to preview the view for the frontpage (/admin/structure/views/edit/frontpage) I get a white screen with following message:

[{"command":"settings","settings":{"basePath":"\/","views":{"ajax_path":"\/views\/ajax","ajaxViews":[{"view_name":"frontpage","view_display_id":"default","view_args":"","view_path":"admin\/structure\/views\/nojs\/preview\/frontpage\/default","view_base_path":"admin\/structure\/views\/nojs\/preview\/frontpage\/default","view_dom_id":1,"pager_element":0}]}}},{"command":"viewsSetForm","output":"\x3cdiv class=\"views-messages\"\x3e\x3cdiv class=\"messages status\"\x3e\n\x3ch2 class=\"element-invisible\"\x3eStatus message\x3c\/h2\x3e\n \x3cul\x3e\n \x3cli\x3e\x3cem\x3eDebug\x3c\/em\x3e: \x3cem\x3e\x26#039;Views data build time: 1.0900497436523 ms\x26#039;\x3c\/em\x3e in \x3cem\x3e_views_fetch_data()\x3c\/em\x3e (line \x3cem\x3e49\x3c\/em\x3e of \x3cem\x3e\/kunden\/135544_81669\/subdomains\/tddp\/d7\/sites\/all\/modules\/views\/includes\/cache.inc\x3c\/em\x3e).\x3c\/li\x3e\n \x3cli\x3e\x3cem\x3eDebug\x3c\/em\x3e: \x3cem\x3e\x26#039;SELECT node.nid AS nid, node.sticky AS node_sticky, node.created AS node_created\nFROM \n{node} node\nWHERE (( (node.promote \x26lt;\x26gt; 0 = :db_condition_placeholder_0) AND (node.status \x26lt;\x26gt; 0 = :db_condition_placeholder_1) ))\nORDER BY node_sticky DESC, node_created DESC\x26#039;\x3c\/em\x3e in \x3cem\x3eviews_plugin_query_default-\x26gt;execute()\x3c\/em\x3e (line \x3cem\x3e1086\x3c\/em\x3e of \x3cem\x3e\/kunden\/135544_81669\/subdomains\/tddp\/d7\/sites\/all\/modules\/views\/plugins\/views_plugin_query_default.inc\x3c\/em\x3e).\x3c\/li\x3e\n \x3c\/ul\x3e\n\x3c\/div\x3e\n\x3c\/div\x3e\x3cform action=\"\/admin\/structure\/views\/nojs\/preview\/frontpage\" accept-charset=\"UTF-8\" method=\"post\" id=\"views-ui-preview-form\" class=\"clearfix\"\x3e\n\x3cdiv\x3e\x3cdiv class=\"form-item form-type-select form-item-display-id\"\x3e\n \x3clabel for=\"preview-display-id\"\x3eDisplay \x3c\/label\x3e\n \x3cselect name=\"display_id\" class=\"form-select\" id=\"preview-display-id\" \x3e\x3coption value=\"default\" selected=\"selected\"\x3eStandard\x3c\/option\x3e\x3coption value=\"page\"\x3ePage\x3c\/option\x3e\x3coption value=\"feed\"\x3eFeed\x3c\/option\x3e\x3c\/select\x3e\n\x3c\/div\x3e\n\x3cdiv class=\"form-item form-type-textfield form-item-args\"\x3e\n \x3clabel for=\"preview-args\"\x3eArguments \x3c\/label\x3e\n \x3cinput type=\"text\" maxlength=\"128\" name=\"args\" id=\"preview-args\" size=\"60\" value=\"\" class=\"form-text\" \/\x3e\n \x3cdiv class=\"description\"\x3eSeparate arguments with a \/ as though they were a URL path.\x3c\/div\x3e\n\x3c\/div\x3e\n\x3cinput type=\"submit\" name=\"op\" id=\"preview-submit\" value=\"Preview\" class=\"form-submit\" \/\x3e\n\x3cinput type=\"hidden\" name=\"form_build_id\" id=\"form-be745bef07c51923541019fc85d3db8e\" value=\"form-be745bef07c51923541019fc85d3db8e\" \/\x3e\n\x3cinput type=\"hidden\" name=\"form_token\" id=\"edit-views-ui-preview-form-form-token\" value=\"e418c860262f8354efedc92c01ee193d\" \/\x3e\n\x3cinput type=\"hidden\" name=\"form_id\" id=\"edit-views-ui-preview-form\" value=\"views_ui_preview_form\" \/\x3e\n\n\x3c\/div\x3e\x3c\/form\x3e\n\x3cdiv class=\"view view-frontpage view-id-frontpage view-display-id-default view-dom-id-1\"\x3e\n \x3cdiv class=\"views-admin-links views-hide\"\x3e\n \x3cul class=\"links\"\x3e\x3cli class=\"0 first\"\x3e\x3ca href=\"\/admin\/structure\/views\/edit\/frontpage?destination=admin\/structure\/views\/nojs\/preview\/frontpage\/default#views-tab-default\"\x3eEdit\x3c\/a\x3e\x3c\/li\x3e\n\x3cli class=\"1\"\x3e\x3ca href=\"\/admin\/structure\/views\/export\/frontpage\"\x3eExport\x3c\/a\x3e\x3c\/li\x3e\n\x3cli class=\"2 last\"\x3e\x3ca href=\"\/admin\/structure\/views\/clone\/frontpage\"\x3eClone\x3c\/a\x3e\x3c\/li\x3e\n\x3c\/ul\x3e \x3c\/div\x3e\n \n \n \n \n \n \n \n \n \x3cdiv class=\"feed-icon\"\x3e\n \x3ca href=\"\/rss.xml\" title=\"Subscribe to Front page feed\" class=\"feed-icon\"\x3e\x3cimg src=\"http:\/\/d7.tddp.de\/misc\/feed.png\" alt=\"Subscribe to Front page feed\" title=\"\" width=\"16\" height=\"16\" \/\x3e\x3c\/a\x3e \x3c\/div\x3e\n \n\x3c\/div\x3e \x3cdiv class=\"views-query-info\"\x3e\x3ctable\x3e\n\x3ctbody\x3e\n \x3ctr class=\"odd\"\x3e\x3ctd\x3e\x3cstrong\x3eQuery\x3c\/strong\x3e\x3c\/td\x3e\x3ctd\x3e\x3cpre\x3eSELECT node.nid AS nid, node.sticky AS node_sticky, node.created AS node_created\nFROM \n{node} node\nWHERE (( (node.promote \x26lt;\x26gt; 0 = :db_condition_placeholder_0) AND (node.status \x26lt;\x26gt; 0 = :db_condition_placeholder_1) ))\nORDER BY node_sticky DESC, node_created DESC\x3c\/pre\x3e\x3c\/td\x3e \x3c\/tr\x3e\n \x3ctr class=\"even\"\x3e\x3ctd\x3e\x3cstrong\x3eTitle\x3c\/strong\x3e\x3c\/td\x3e\x3ctd\x3eDies ist der Titel\x3c\/td\x3e \x3c\/tr\x3e\n \x3ctr class=\"odd\"\x3e\x3ctd\x3e\x3cstrong\x3ePath\x3c\/strong\x3e\x3c\/td\x3e\x3ctd\x3eThis display has no path.\x3c\/td\x3e \x3c\/tr\x3e\n \x3ctr class=\"even\"\x3e\x3ctd\x3e\x3cstrong\x3eQuery build time\x3c\/strong\x3e\x3c\/td\x3e\x3ctd\x3e2.99 ms\x3c\/td\x3e \x3c\/tr\x3e\n \x3ctr class=\"odd\"\x3e\x3ctd\x3e\x3cstrong\x3eQuery execute time\x3c\/strong\x3e\x3c\/td\x3e\x3ctd\x3e21.56 ms\x3c\/td\x3e \x3c\/tr\x3e\n \x3ctr class=\"even\"\x3e\x3ctd\x3e\x3cstrong\x3eView render time\x3c\/strong\x3e\x3c\/td\x3e\x3ctd\x3e3.76 ms\x3c\/td\x3e \x3c\/tr\x3e\n\x3c\/tbody\x3e\n\x3c\/table\x3e\n\x3c\/div\x3e","title":"Dies ist der Titel"}]