diff --git a/calendar/inc/class.uicalendar.inc.php b/calendar/inc/class.uicalendar.inc.php
index 68eeceeb69..ba1536fbf7 100755
--- a/calendar/inc/class.uicalendar.inc.php
+++ b/calendar/inc/class.uicalendar.inc.php
@@ -1302,9 +1302,21 @@
 				// Construct Participants stack
 				$_stack_participants = $GLOBALS['phpgw']->session->appsession("participants");
 				if($matrix_mode == 1) // You come from matrix, ok
-					$_stack_participants .= ";" . $GLOBALS['phpgw']->session->appsession("participants_matrix");
+				{
+					// protection
+					if($_stack_participants)
+						$_stack_participants .= ";";
+
+					$_stack_participants .= $GLOBALS['phpgw']->session->appsession("participants_matrix");
+				}
 				if( get_var('owner',array('GET'),FALSE) )
-					$_stack_participants .= ";" . str_replace(",", ";", get_var('owner', array('GET'), FALSE));
+				{
+					// protection
+					if($_stack_participants)
+						$_stack_participants .= ";";
+
+					$_stack_participants .= str_replace(",", ";", get_var('owner', array('GET'), FALSE));
+				}
 				
 				// Read each participant
 				foreach(explode(";", $_stack_participants) as $part)
diff --git a/calendar/inc/class.uiviews.inc.php b/calendar/inc/class.uiviews.inc.php
index 9a5624ada2..e3ad69d165 100644
--- a/calendar/inc/class.uiviews.inc.php
+++ b/calendar/inc/class.uiviews.inc.php
@@ -336,7 +336,7 @@ class uiviews extends uical
 	{
 		// Get Owner/Participants
 		$_session_data = $GLOBALS['phpgw']->session->appsession("session_data", "calendar");
-		$participants = str_replace(",", ";", $_session_data["owner"]);
+		$participants = $_session_data["owner"];
 		unset($_session_data);
 
 		if ($this->debug > 1 || $this->debug==='timeGridWidget') $this->bo->debug_message('uiviews::timeGridWidget(events=%1,width=%2,granularity_m=%3,px_m=%4,)',True,$daysEvents,$width,$granularity_m,$px_m);