diff --git a/calendar/inc/class.uicalendar.inc.php b/calendar/inc/class.uicalendar.inc.php
index 56ff510185..ee6e11ed87 100755
--- a/calendar/inc/class.uicalendar.inc.php
+++ b/calendar/inc/class.uicalendar.inc.php
@@ -3610,11 +3610,12 @@
 			$starttime = $param['starttime'];
 			$endtime = $param['endtime'];
 			$participants = $param['participants'];
+			$participants_id = array();
 			foreach($participants as $part => $nul)
 			{
 				$participants[$part] = $GLOBALS['phpgw']->common->grab_owner_name($part);
 				// Much better for processor  :)
-				$participants_id[]  .= $part;
+				$participants_id[] = $part;
 			}
 			uasort($participants,'strnatcasecmp');	// sort them after their fullname
 
@@ -3641,7 +3642,7 @@
 					$k = ($j == 0 ? sprintf('%02d',$i).'<br>':'').sprintf('%02d',$j*$increment);
 
 					$str .= '<td align="left" bgcolor="'.$this->theme['bg_color'].'"><font color="'.$phpgw_info['theme']['bg_text'].'" face="'.$this->theme['font'].'" size="-2">'
-						. '<a href="'.$this->page('add','&date='.$date['full'].'&hour='.$i.'&minute='.(interval * $j) . '&participants=' . base64_encode(implode(";", $participants_id)) )."\" onMouseOver=\"window.status='".$i.':'.(($increment * $j)<=9?'0':'').($increment * $j)."'; return true;\">"
+						. '<a href="'.$this->page('add','&date='.$date['full'].'&hour='.$i.'&minute='.(interval * $j) . '&participants=' . base64_encode(implode(';', $participants_id)) )."\" onMouseOver=\"window.status='".$i.':'.(($increment * $j)<=9?'0':'').($increment * $j)."'; return true;\">"
 						. $k."</a>&nbsp;</font></td>\n";
 				}
 			}