diff --git a/lib/file_wopi.php b/lib/file_wopi.php
index dd82429..2e95374 100644
--- a/lib/file_wopi.php
+++ b/lib/file_wopi.php
@@ -1,312 +1,318 @@
 <?php
 /**
  +--------------------------------------------------------------------------+
  | This file is part of the Kolab File API                                  |
  |                                                                          |
  | Copyright (C) 2012-2016, Kolab Systems AG                                |
  |                                                                          |
  | This program is free software: you can redistribute it and/or modify     |
  | it under the terms of the GNU Affero General Public License as published |
  | by the Free Software Foundation, either version 3 of the License, or     |
  | (at your option) any later version.                                      |
  |                                                                          |
  | This program is distributed in the hope that it will be useful,          |
  | but WITHOUT ANY WARRANTY; without even the implied warranty of           |
  | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the             |
  | GNU Affero General Public License for more details.                      |
  |                                                                          |
  | You should have received a copy of the GNU Affero General Public License |
  | along with this program. If not, see <http://www.gnu.org/licenses/>      |
  +--------------------------------------------------------------------------+
  | Author: Aleksander Machniak <machniak@kolabsys.com>                      |
  +--------------------------------------------------------------------------+
 */
 
 /**
  * Document editing sessions handling (WOPI)
  */
 class file_wopi extends file_document
 {
     protected $cache;
 
     // Mimetypes supported by CODE, but not advertised by all possible names
     protected $aliases = array(
         'application/vnd.corel-draw' => 'image/x-coreldraw',
     );
 
     /**
      * Return viewer URI for specified file/session. This creates
      * a new collaborative editing session when needed.
      *
      * @param string $file        File path
      * @param array  &$file_info  File metadata (e.g. type)
      * @param string &$session_id Optional session ID to join to
      * @param string $readonly    Create readonly (one-time) session
      *
      * @return string WOPI URI for specified document
      * @throws Exception
      */
     public function session_start($file, &$file_info, &$session_id = null, $readonly = false)
     {
         parent::session_start($file, $file_info, $session_id, $readonly);
 
         if ($session_id) {
             // Create Chwala session for use as WOPI access_token
             // This session will have access to this one document session only
             $keys = array('env', 'user_id', 'user', 'username', 'password',
                 'storage_host', 'storage_port', 'storage_ssl');
 
             $data = array_intersect_key($_SESSION, array_flip($keys));
             $data['document_session'] = $session_id;
 
             $this->token = $this->api->session->create($data);
         }
 
         return $this->frame_uri($session_id, $file_info['type']);
     }
 
     /**
      * Generate URI of WOPI editing session (WOPIsrc)
      */
     protected function frame_uri($id, $mimetype)
     {
         $capabilities = $this->capabilities();
 
         if (empty($capabilities) || empty($mimetype)) {
             return;
         }
 
         $metadata = $capabilities[strtolower($mimetype)];
 
         if (empty($metadata)) {
             return;
         }
 
         $office_url   = rtrim($metadata['urlsrc'], ' /?'); // collabora
         $service_url  = rtrim($this->rc->config->get('fileapi_wopi_service'), ' /'); // kolab-wopi
         $service_url .= '/wopi/files/' . $id;
 
         // @TODO: Parsing and replacing placeholder values
         // https://wopi.readthedocs.io/en/latest/discovery.html#action-urls
 
         $args = array('WOPISrc' => $service_url);
 
         // We could also set: title, closebutton, revisionhistory
         // @TODO: do it in editor_post_params() when supported by the editor
         if ($lang = $this->api->env['language']) {
             $args['lang'] = str_replace('_', '-', $lang);
         }
 
         return $office_url . '?' . http_build_query($args, '', '&');
     }
 
     /**
      * Retern extra viewer parameters to post to the viewer iframe
      *
      * @param array $info File info
      *
      * @return array POST parameters
      */
     public function editor_post_params($info)
     {
         // Access token TTL (number of milliseconds since January 1, 1970 UTC)
         if ($ttl = $this->rc->config->get('session_lifetime', 0) * 60) {
             $now = new DateTime('now', new DateTimeZone('UTC'));
             $ttl = ($ttl + $now->format('U')) . '000';
         }
 
         $params = array(
             'access_token'     => $this->token,
             'access_token_ttl' => $ttl ?: 0,
         );
 
         return $params;
     }
 
     /**
      * List supported mimetypes
      *
      * @param bool $editable Return only editable mimetypes
      *
      * @return array List of supported mimetypes
      */
     public function supported_filetypes($editable = false)
     {
         $caps = $this->capabilities();
 
         if ($editable) {
             $editable = array();
             foreach ($caps as $mimetype => $c) {
                 if ($c['name'] == 'edit') {
                     $editable[] = $mimetype;
                 }
             }
 
             return $editable;
         }
 
         return array_keys($caps);
     }
 
     /**
      * Uses WOPI discovery to get Office capabilities
      * https://wopi.readthedocs.io/en/latest/discovery.html
      */
     protected function capabilities()
     {
         $cache_key = 'wopi.capabilities';
         if ($result = $this->get_from_cache($cache_key)) {
             return $this->apply_aliases($result);
         }
 
         $office_url  = rtrim($this->rc->config->get('fileapi_wopi_office'), ' /');
         $office_url .= '/hosting/discovery';
 
         try {
             $request = $this->http_request();
             $request->setMethod(HTTP_Request2::METHOD_GET);
             $request->setBody('');
             $request->setUrl($office_url);
 
             $response = $request->send();
             $body     = $response->getBody();
             $code     = $response->getStatus();
 
             if (empty($body) || $code != 200) {
                 throw new Exception("Unexpected WOPI discovery response");
             }
         }
         catch (Exception $e) {
-            rcube::raise_error($e, true, true);
+            rcube::raise_error($e, true, false);
+
+            // Don't bail out here, it would make the kolab_files UI broken
+            return array();
         }
 
         // parse XML output
         // <wopi-discovery>
         //   <net-zone name="external-http">
         //     <app name="application/vnd.lotus-wordpro">
         //       <action ext="lwp" name="edit" urlsrc="https://office.example.org/loleaflet/1.8.3/loleaflet.html?"/>
         //     </app>
         // ...
 
         $node = new DOMDocument('1.0', 'UTF-8');
         $node->loadXML($body);
 
         $result = array();
 
         foreach ($node->getElementsByTagName('app') as $app) {
             if ($mimetype = $app->getAttribute('name')) {
                 if ($action = $app->getElementsByTagName('action')->item(0)) {
                     foreach ($action->attributes as $attr) {
                         $result[$mimetype][$attr->name] = $attr->value;
                     }
                 }
             }
         }
 
         if (empty($result)) {
-            rcube::raise_error("Failed to parse WOPI discovery response: $body", true, true);
+            rcube::raise_error("Failed to parse WOPI discovery response: $body", true, false);
+
+            // Don't bail out here, it would make the kolab_files UI broken
+            return array();
         }
 
         $this->save_in_cache($cache_key, $result);
 
         return $this->apply_aliases($result);
     }
 
     /**
      * Initializes HTTP request object
      */
     protected function http_request()
     {
         require_once 'HTTP/Request2.php';
 
         $request = new HTTP_Request2();
 
         // Configure connection options
         $config      = $this->rc->config;
         $http_config = (array) $config->get('http_request', $config->get('kolab_http_request'));
 
         // Deprecated config, all options are separated variables
         if (empty($http_config)) {
             $options = array(
                 'ssl_verify_peer',
                 'ssl_verify_host',
                 'ssl_cafile',
                 'ssl_capath',
                 'ssl_local_cert',
                 'ssl_passphrase',
                 'follow_redirects',
             );
 
             foreach ($options as $optname) {
                 if (($optvalue = $config->get($optname)) !== null
                     || ($optvalue = $config->get('kolab_' . $optname)) !== null
                 ) {
                     $http_config[$optname] = $optvalue;
                 }
             }
         }
 
         if (!empty($http_config)) {
             try {
                 $request->setConfig($http_config);
             }
             catch (Exception $e) {
                 rcube::log_error("HTTP: " . $e->getMessage());
             }
         }
 
         // proxy User-Agent
         $request->setHeader('user-agent', $_SERVER['HTTP_USER_AGENT']);
 
         // some HTTP server configurations require this header
         $request->setHeader('accept', "application/json,text/javascript,*/*");
 
         return $request;
     }
 
     /**
      * Get cached data
      */
     protected function get_from_cache($key)
     {
         if ($cache = $this->get_cache()) {
             return $cache->get($key);
         }
     }
 
     /**
      * Store data in cache
      */
     protected function save_in_cache($key, $value)
     {
         if ($cache = $this->get_cache()) {
             $cache->set($key, $value);
         }
     }
 
     /**
      * Getter for the shared cache engine object
      */
     protected function get_cache()
     {
         if ($this->cache === null) {
             $this->cache = $this->rc->get_cache_shared('fileapi') ?: false;
         }
 
         return $this->cache;
     }
 
     /**
      * Support more mimetypes in CODE capabilities
      */
     protected function apply_aliases($caps)
     {
         foreach ($this->aliases as $type => $alias) {
             if (isset($caps[$type]) && !isset($caps[$alias])) {
                 $caps[$alias] = $caps[$type];
             }
         }
 
         return $caps;
     }
 }