If Click submenu under Main Menu new window is not opening in IE9 version

function openUst(existingMenu){
if (document.all[ existingMenu + 'Ust'].style.color != "graytext"){
window.open('/common/pgAdmSessionMonitor.jsp','sitwin','height=500,width=800,toolbar=no');
}
alert("End openUst()");
}

<DIV id="mainUst" STYLE="position:relative; top:0; left:0; background-color:threedface; border-left:1px solid white; height:20px; color:<%=adminMenuColor%>; font-family:MS Sans Serif; font-weight:normal; padding:2px; padding-left:10px; font-size:8pt; cursor:default" onmouseover="this.style.background='threedshadow';" onmouseout="this.style.background='threedface';"
onclick="parent.openUst('main')">
&nbsp;&nbsp;Online User Tracking</DIV>

Is anything wrong or any suggestions Please......


-Thanks in advance
Vijay