diff --git a/addressbook/inc/class.addressbook_groupdav.inc.php b/addressbook/inc/class.addressbook_groupdav.inc.php
index 70ae27d8b8..c0a02124f9 100644
--- a/addressbook/inc/class.addressbook_groupdav.inc.php
+++ b/addressbook/inc/class.addressbook_groupdav.inc.php
@@ -392,9 +392,17 @@ class addressbook_groupdav extends groupdav_handler
 		if ($GLOBALS['egw_info']['user']['preferences']['addressbook']['hide_accounts']) $filter['account_id'] = null;
 
 		$result = $this->bo->search(array(),'MAX(contact_modified) AS contact_modified','','','',false,'AND',false,$filter);
-
-		$ctag = 'EGw-'.$result[0]['contact_modified'].'-wGE';
-		return $ctag;
+		
+		if (empty($result))
+		{
+			$ctag = $result[0]['contact_modified'];
+		}
+		else
+		{
+			$ctag = time();
+		}
+				
+		return 'EGw-'.$ctag.'-wGE';
 	}
 
 	/**
diff --git a/calendar/inc/class.calendar_groupdav.inc.php b/calendar/inc/class.calendar_groupdav.inc.php
index f534b2f1d1..2ce33651ef 100644
--- a/calendar/inc/class.calendar_groupdav.inc.php
+++ b/calendar/inc/class.calendar_groupdav.inc.php
@@ -758,34 +758,11 @@ error_log(__METHOD__."($path,,".array2string($start).") filter=".array2string($f
 	 */
 	public function getctag($path,$user)
 	{
-		if ($this->debug > 1) error_log(__FILE__.'['.__LINE__.'] '.__METHOD__. "($path)[$user]");
+		$ctag = $GLOBALS['egw']->contenthistory->getLastChange('calendar');
+
+		if ($this->debug > 1) error_log(__FILE__.'['.__LINE__.'] '.__METHOD__. "($path)[$user] = $ctag");
 		
-		$filter = array(
-			'users' => $user,
-			'start' => time()-100*24*3600,	// default one month back -30 breaks all sync recurrences
-			'end' => time()+365*24*3600,	// default one year into the future +365
-			'enum_recuring' => false,
-			'daywise' => false,
-			'date_format' => 'server',
-			'order' => 'cal_modified DESC,cal_etag DESC',
-			'offset' => 0,
-			'num_rows'	=> 1,
-		);
-
-		if (strpos($path, '/calendar') === 0)
-		{
-			$filter['filter'] = 'owner';
-		}
-		else
-		{
-			$filter['filter'] = 'default'; // not rejected
-		}
-
-		$result =& $this->bo->search($filter);
-
-		$entry = array_shift($result);
-
-		return $this->get_etag($entry);
+		return 'EGw-'.$ctag.'-wGE';
 	}
 
 	/**
diff --git a/infolog/inc/class.infolog_groupdav.inc.php b/infolog/inc/class.infolog_groupdav.inc.php
index b50c135568..7f2b792af7 100644
--- a/infolog/inc/class.infolog_groupdav.inc.php
+++ b/infolog/inc/class.infolog_groupdav.inc.php
@@ -512,6 +512,8 @@ class infolog_groupdav extends groupdav_handler
 		);
 
 		$result =& $this->bo->search($query);
+		
+		if (empty($result)) return 'EGw-'.time().'-wGE';
 
 		$entry = array_shift($result);
 
diff --git a/phpgwapi/inc/class.contenthistory.inc.php b/phpgwapi/inc/class.contenthistory.inc.php
index 2c0ad1f5f7..36c49c2a5f 100644
--- a/phpgwapi/inc/class.contenthistory.inc.php
+++ b/phpgwapi/inc/class.contenthistory.inc.php
@@ -170,4 +170,32 @@ class contenthistory
 		}
 		return true;
 	}
+	
+	/**
+	 * get the timestamp of last change for appname
+	 *
+	 * find which content changed since $_ts for application $_appName
+	 *
+	 * @param string$_appName the appname example: infolog_notes
+	 * 
+	 * @return timestamp of last change for this application
+	 */
+	function getLastChange($_appName)
+	{
+		$max = 0;
+		
+		$where = array('sync_appname' => $_appName);
+
+		foreach (array('modified','deleted','added') as $action)
+		{
+			if (($ts = $this->db->select(self::TABLE,'MAX(sync_'.$action.')',$where,__LINE__,__FILE__)->fetchColumn()))
+			{
+				$ts = $this->db->from_timestamp($ts);
+				if ($ts > $max) $max = $ts;
+			}
+		}
+			
+		return $max;
+	}
+	
 }