diff --git a/lib/Kolab/CalDAV/Calendar.php b/lib/Kolab/CalDAV/Calendar.php
index a8a4381..3e34190 100644
--- a/lib/Kolab/CalDAV/Calendar.php
+++ b/lib/Kolab/CalDAV/Calendar.php
@@ -1,174 +1,174 @@
 <?php
 
 /**
  * SabreDAV Calendar derived class to encapsulate a Kolab storage folder
  *
  * @author Thomas Bruederli <bruederli@kolabsys.com>
  *
  * Copyright (C) 2013, Kolab Systems AG <contact@kolabsys.com>
  *
  * 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/>.
  */
 
 namespace Kolab\CalDAV;
 
 use \PEAR;
 use \kolab_storage;
 use Sabre\CalDAV\Backend;
 
 /**
  * This object represents a CalDAV calendar.
  *
  * A calendar can contain multiple TODO and or Events. These are represented
  * as \Sabre\CalDAV\CalendarObject objects.
  */
 class Calendar extends \Sabre\CalDAV\Calendar
 {
     public $id;
     public $storage;
     public $ready = false;
 
 
     /**
      * Default constructor
      */
     public function __construct(Backend\BackendInterface $caldavBackend, $calendarInfo)
     {
         parent::__construct($caldavBackend, $calendarInfo);
 
         $this->id = $calendarInfo['id'];
         $this->storage = $caldavBackend->get_storage_folder($this->id);
         $this->ready = is_object($this->storage) && is_a($this->storage, 'kolab_storage_folder');
     }
 
 
     /**
      * Returns the owner principal
      *
      * This must be a url to a principal, or null if there's no owner
      *
      * @return string|null
      */
     public function getOwner()
     {
         if ($this->storage->get_namespace() == 'personal') {
             return $this->calendarInfo['principaluri'];
         }
         else {
             return 'principals/' . $this->storage->get_owner();
         }
     }
 
 
     /**
      * Returns a list of ACE's for this node.
      *
      * Each ACE has the following properties:
      *   - 'privilege', a string such as {DAV:}read or {DAV:}write. These are currently the only supported privileges
      *   - 'principal', a url to the principal who owns the node
      *   - 'protected' (optional), indicating that this ACE is not allowed to be updated.
      *
      * @return array
      */
     public function getACL()
     {
         // return ACL information based on IMAP MYRIGHTS
         $rights = $this->storage->get_myrights();
-        if ($rights && !PEAR::isError($rights)) {
+        if ($rights && !is_a($rights, 'PEAR_Error')) {
             // user has at least read access to calendar folders listed
             $acl = array(
                 array(
                     'privilege' => '{DAV:}read',
                     'principal' => $this->calendarInfo['principaluri'],
                     'protected' => true,
                 ),
             );
 
             $owner = $this->getOwner();
             $is_owner = $owner == $this->calendarInfo['principaluri'];
 
             if ($is_owner || strpos($rights, 'i') !== false) {
                 $acl[] = array(
                     'privilege' => '{DAV:}write',
                     'principal' => $this->calendarInfo['principaluri'],
                     'protected' => true,
                 );
             }
 
             return $acl;
         }
         else {
             // fallback to default ACL rules based on ownership
             return parent::getACL();
         }
     }
 
     /**
      * This method returns the ACL's for calendar objects in this calendar.
      * The result of this method automatically gets passed to the
      * calendar-object nodes in the calendar.
      *
      * @return array
      */
     function getChildACL()
     {
         static $myacl;
 
         $acl = [
             [
                 'privilege' => '{DAV:}read',
                 'principal' => $this->calendarInfo['principaluri'],
                 'protected' => true,
             ],
             [
                 'privilege' => '{DAV:}read',
                 'principal' => $this->calendarInfo['principaluri'] . '/calendar-proxy-write',
                 'protected' => true,
             ],
             [
                 'privilege' => '{DAV:}read',
                 'principal' => $this->calendarInfo['principaluri'] . '/calendar-proxy-read',
                 'protected' => true,
             ],
         ];
 
         if (empty($this->calendarInfo['{http://sabredav.org/ns}read-only'])) {
             // check write privileges of address book node
             if (!$myacl) {
                 $myacl = $this->getACL();
             }
 
             $write = false;
             array_walk($myacl, function($acl, $i) use (&$write) {
                 if ($acl['privilege'] == '{DAV:}write') {
                     $write = true;
                 }
             });
 
             if ($write) {
                 $acl[] = [
                     'privilege' => '{DAV:}write',
                     'principal' => $this->calendarInfo['principaluri'],
                     'protected' => true,
                 ];
                 $acl[] = [
                     'privilege' => '{DAV:}write',
                     'principal' => $this->calendarInfo['principaluri'] . '/calendar-proxy-write',
                     'protected' => true,
                 ];
             }
         }
         return $acl;
     }
 }
diff --git a/lib/Kolab/CardDAV/AddressBook.php b/lib/Kolab/CardDAV/AddressBook.php
index 508b6cb..33bfe19 100644
--- a/lib/Kolab/CardDAV/AddressBook.php
+++ b/lib/Kolab/CardDAV/AddressBook.php
@@ -1,184 +1,184 @@
 <?php
 
 /**
  * SabreDAV AddressBook derived class to encapsulate a Kolab storage folder
  *
  * @author Thomas Bruederli <bruederli@kolabsys.com>
  *
  * Copyright (C) 2013, Kolab Systems AG <contact@kolabsys.com>
  *
  * 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/>.
  */
 
 namespace Kolab\CardDAV;
 
 use \PEAR;
 use Sabre\DAV;
 use Sabre\DAVACL;
 use Sabre\CardDAV\Backend;
 
 /**
  * The AddressBook class represents a CardDAV addressbook, owned by a specific user
  *
  */
 class AddressBook extends \Sabre\CardDAV\AddressBook implements \Sabre\CardDAV\IAddressBook, DAV\IProperties, DAVACL\IACL
 {
     public $id;
     public $storage;
     public $ready = false;
 
 
     /**
      * Constructor
      *
      * @param Backend\BackendInterface $carddavBackend
      * @param array $addressBookInfo
      */
     public function __construct(Backend\BackendInterface $carddavBackend, array $addressBookInfo)
     {
         parent::__construct($carddavBackend, $addressBookInfo);
 
         $this->id = $addressBookInfo['id'];
 
         if ($this->id == '__all__') {
             $this->ready = true;
         }
         else {
             $this->storage = $carddavBackend->get_storage_folder($this->id);
             $this->ready = is_object($this->storage) && is_a($this->storage, 'kolab_storage_folder');
         }
     }
 
 
     /**
      * Renames the addressbook
      *
      * @param string $newName
      * @return void
      */
     public function setName($newName)
     {
         // TODO: implement this
         throw new DAV\Exception\MethodNotAllowed('Renaming addressbooks is not yet supported');
     }
 
 
     /**
      * Returns the owner principal
      *
      * This must be a url to a principal, or null if there's no owner
      *
      * @return string|null
      */
     public function getOwner()
     {
         if (!$this->storage || $this->storage->get_namespace() == 'personal') {
             return $this->addressBookInfo['principaluri'];
         }
         else {
             return 'principals/' . $this->storage->get_owner();
         }
     }
 
     /**
      * Returns a card
      *
      * @param string $name
      * @return \ICard
      *
     public function getChild($name)
     {
         $obj = $this->carddavBackend->getCard($this->addressBookInfo['id'], $name);
         if (!$obj) throw new DAV\Exception\NotFound('Card not found');
         return new Card($this->carddavBackend,$this->addressBookInfo, $obj);
     }*/
 
     /**
      * Returns a list of ACE's for this node.
      *
      * Each ACE has the following properties:
      *   * 'privilege', a string such as {DAV:}read or {DAV:}write. These are
      *     currently the only supported privileges
      *   * 'principal', a url to the principal who owns the node
      *   * 'protected' (optional), indicating that this ACE is not allowed to
      *      be updated.
      *
      * @return array
      */
     public function getACL()
     {
         // return ACL information based on IMAP MYRIGHTS
         $rights = $this->storage ? $this->storage->get_myrights() : null;
-        if ($rights && !PEAR::isError($rights)) {
+        if ($rights && !is_a($rights, 'PEAR_Error')) {
             // user has at least read access to calendar folders listed
             $acl = array(
                 array(
                     'privilege' => '{DAV:}read',
                     'principal' => $this->addressBookInfo['principaluri'],
                     'protected' => true,
                 ),
             );
 
             $owner = $this->getOwner();
             $is_owner = $owner == $this->addressBookInfo['principaluri'];
 
             if ($is_owner || strpos($rights, 'i') !== false) {
                 $acl[] = array(
                     'privilege' => '{DAV:}write',
                     'principal' => $this->addressBookInfo['principaluri'],
                     'protected' => true,
                 );
             }
 
             return $acl;
         }
         else {
             // fallback to default ACL rules based on ownership
             return parent::getACL();
         }
     }
 
     /**
      * Updates the ACL
      *
      * This method will receive a list of new ACE's.
      *
      * @param array $acl
      * @return void
      */
     public function setACL(array $acl)
     {
         // TODO: implement this
         throw new DAV\Exception\MethodNotAllowed('Changing ACL is not yet supported');
     }
 
     /**
      * This method returns the ACL's for card nodes in this address book.
      * The result of this method automatically gets passed to the
      * card nodes in this address book.
      *
      * @return array
      */
     function getChildACL()
     {
         static $myacl;
 
         if (!$myacl) {
             $myacl = $this->getACL();
         }
 
         return $myacl;
     }
 
 }